UK: English High Court Provides Guidance On When A Common Mistake Will Render A Contract Void

Last Updated: 10 July 2018
Article by Susan Rosser and Robert Hobson


One of the most fundamental purposes (and indeed contractual legal principles) of a contract is that its terms should be certain, such that each party to the contract knows what it is signing up to and the terms by which it must abide. However, in some instances, it may be the case that the parties agree to the terms of a contract on the basis of a shared mistaken assumption about a fact which is integral to the contract. In such circumstances, the equitable doctrine of "common mistake" may be used as a defence and, if successful, render the contract void.

In the recent case of Triple Seven MSN 27251 Limited & another v Azman Air Services Limited1, the English High Court held that the doctrine of "common mistake" did not apply and the contracts in question were not void. In reaching its decision, the court provided some useful guidance on how this doctrine will be assessed and applied by the English courts.


Two members of the Triple Seven group of aircraft leasing companies (the "Claimants") entered into two five-year aircraft leases with Azman Air Services Limited (the "Defendant"), whereby the Defendant would rent two Boeing 777 airliners. It was understood by the parties that the aircraft would be used to transport passengers from Nigeria to Saudi Arabia for the Hajj and Umrah pilgrimages. However, hours after signing the contracts, the Defendant received a letter from the General Authority of Civil Aviation of Saudi Arabia (the "GACA") excluding it from participating in the 2016 Hajj airlift.

Within the first two weeks of executing the contracts, the Claimants tendered the aircraft for delivery to the Defendant. However, the Defendant refused to accept delivery of the aircraft on the basis that it was no longer able to participate in the 2016 Hajj airlift. The Claimants therefore terminated the leases and sued for damages arising from the Defendant's non-performance of such leases.

The Defendants had pleaded a number of defences to this claim but, by the time of the trial, the only substantive defence advanced was that the lease agreements were void at common law for "common mistake".

The High Court's analysis of the defence of common mistake

In his judgment, the judge considered the test for common mistake, as had been stated and clarified by the Court of Appeal in Great Peace Shipping Ltd v Tsavliris Salvage (International ) Ltd2. In that case, the court held that the mistaken common assumption between the parties must "render the performance of the contract impossible". That case had, in turn, elaborated on the previous decision in Associated Japanese Bank (International) Ltd v Credit du Nord SA3, which had considered that the relevant mistake must have rendered the subject matter of the contract "essentially and radically different from the subject matter which the parties believed to exist".

In the present case, the judge noted a previous attempt to reconcile these two differing formulations of the test4 but acknowledged that some adjustment was necessary. He considered that the most appropriate test for determining the application of the doctrine of "common mistake" is to: (a) assess the fundamental nature of the shared assumption to the contract; and (b) compare the disparity between the assumed state of affairs and the actual state of affairs and analyse whether that disparity is sufficiently fundamental or essential or radical.

More specifically, the judge used the existing case law to break down that test into the following consolidated set of six key principles:

  1. at the time the contract was executed, the parties must have substantially shared an assumption as to the existence of a state of affairs;
  2. the assumption itself must have been fundamental to the contract;
  3. the assumption must have been incorrect at the time the contract was executed;
  4. by reason of the assumption being incorrect, the contract or its performance would be essentially and radically different from what the parties believed to be the case at the time the contract was executed, or the contract must be impossible to perform having regard to the common assumption. Put another way, there must be a fundamental difference between the assumed and actual state of affairs;
  5. the parties, or at least the party relying on the common mistake, would not have entered into the contract had the parties been aware that the common assumption was incorrect; and
  6. the contract must not have made provision in the event that the common assumption was mistaken.

Were the aircraft leasing contracts rendered void?

Applying the principles described above, the judge concluded that the parties did share an incorrect assumption as to the existence of a state of affairs, as per items (a) and (c) above. More specifically, this was that the parties had entered into the lease agreements on the assumption that the Defendant expected to obtain approval from the GACA to participate in the 2016 Hajj airlift. This approval had in fact been refused prior to the execution of the contract, albeit that the Defendant was not aware of this at that time.

However, this in itself was of course insufficient for the doctrine of "common mistake" to apply. The additional principles needed to be considered and, in doing so, the judge held that the mistaken assumptions shared by the parties did not make the lease agreements void, because they:

  1. were not "sufficiently fundamental" to the lease agreements (item (b) above);
  2. did not make the lease agreements "essentially and radically different" from what the parties understood them to be (item (d) above); and
  3. did not make the lease agreements "impossible to perform" (also item (d) above).

In forming these conclusions, the judge explained that the lease agreements were each for a period of five years and, therefore, the 2016 Hajj airlift represented only "a relatively short period of the entire lease period as a whole". As such, the revenue earned from participating in the Hajj airlift was not fundamental to the performance of the leases, as there remained "a substantial profit to be earned" in subsequent years. It therefore remained possible for the parties to perform the lease agreements even without the defendant's participation in the 2016 Hajj airlift.

In addition, even if the mistaken common assumption had been "sufficiently fundamental" and/or led to the lease agreements being "essentially and radically different", the lease agreements had provided that the Defendant's obligations were "absolute and unconditional, irrespective of any contingency or circumstance whatsoever...". As such, the parties had allocated the risk of the failure to obtain the GACA's approval to the Defendant. Item (f) above had therefore not been satisfied and this in itself would have been enough to prevent the doctrine from applying and the contract being voidable.


Although this case turns on its specific facts, the decision is useful in providing a distilled and codified list of principles which can be used to assess whether the equitable doctrine of "common mistake" will apply. Given the nature of the guidance, and as shown by the outcome of this case, the threshold for relying on this defence is high and it will likely only be in limited circumstances that a contract will be considered void on this ground.

This case is also useful in confirming that the doctrine of "common mistake" will not in any way cut across the principles of contractual certainty. On the one hand, by clarifying that the doctrine will only apply in extreme circumstances, namely where the shared mistaken assumption is, amongst other things, "sufficiently fundamental" to the contract, the value of certainty attached to a contract is not, as noted by the judge, "unjustifiably undermined". However, equally, this decision also ensures that where a mistaken belief would lead to a material injustice to one or either of the parties (on the basis of the principles set out in the judgment), this will be remedied by voiding the contract. This, therefore, strikes a fair balance between protecting the certainty of the contractual terms and avoiding any undue prejudice to the parties caused as a result of the mistaken assumption.


1. [2018] EWHC 1348 (Comm).

2. [2002] EWCA Civ 1407.

3. [1989] 1 WLR 255.

4. Apvodedo NV v Collins [2008] EWHC 775 (Ch).

Originally published 29 June 2018

Visit us at

Mayer Brown is a global legal services provider comprising legal practices that are separate entities (the "Mayer Brown Practices"). The Mayer Brown Practices are: Mayer Brown LLP and Mayer Brown Europe – Brussels LLP, both limited liability partnerships established in Illinois USA; Mayer Brown International LLP, a limited liability partnership incorporated in England and Wales (authorized and regulated by the Solicitors Regulation Authority and registered in England and Wales number OC 303359); Mayer Brown, a SELAS established in France; Mayer Brown JSM, a Hong Kong partnership and its associated entities in Asia; and Tauil & Chequer Advogados, a Brazilian law partnership with which Mayer Brown is associated. "Mayer Brown" and the Mayer Brown logo are the trademarks of the Mayer Brown Practices in their respective jurisdictions.

© Copyright 2018. The Mayer Brown Practices. All rights reserved.

This Mayer Brown article provides information and comments on legal issues and developments of interest. The foregoing is not a comprehensive treatment of the subject matter covered and is not intended to provide legal advice. Readers should seek specific legal advice before taking any action with respect to the matters discussed herein.

To print this article, all you need is to be registered on

Click to Login as an existing user or Register so you can print this article.

In association with
Related Topics
Related Articles
Related Video
Up-coming Events Search
Font Size:
Mondaq on Twitter
Mondaq Free Registration
Gain access to Mondaq global archive of over 375,000 articles covering 200 countries with a personalised News Alert and automatic login on this device.
Mondaq News Alert (some suggested topics and region)
Select Topics
Registration (please scroll down to set your data preferences)

Mondaq Ltd requires you to register and provide information that personally identifies you, including your content preferences, for three primary purposes (full details of Mondaq’s use of your personal data can be found in our Privacy and Cookies Notice):

  • To allow you to personalize the Mondaq websites you are visiting to show content ("Content") relevant to your interests.
  • To enable features such as password reminder, news alerts, email a colleague, and linking from Mondaq (and its affiliate sites) to your website.
  • To produce demographic feedback for our content providers ("Contributors") who contribute Content for free for your use.

Mondaq hopes that our registered users will support us in maintaining our free to view business model by consenting to our use of your personal data as described below.

Mondaq has a "free to view" business model. Our services are paid for by Contributors in exchange for Mondaq providing them with access to information about who accesses their content. Once personal data is transferred to our Contributors they become a data controller of this personal data. They use it to measure the response that their articles are receiving, as a form of market research. They may also use it to provide Mondaq users with information about their products and services.

Details of each Contributor to which your personal data will be transferred is clearly stated within the Content that you access. For full details of how this Contributor will use your personal data, you should review the Contributor’s own Privacy Notice.

Please indicate your preference below:

Yes, I am happy to support Mondaq in maintaining its free to view business model by agreeing to allow Mondaq to share my personal data with Contributors whose Content I access
No, I do not want Mondaq to share my personal data with Contributors

Also please let us know whether you are happy to receive communications promoting products and services offered by Mondaq:

Yes, I am happy to received promotional communications from Mondaq
No, please do not send me promotional communications from Mondaq
Terms & Conditions (the Website) is owned and managed by Mondaq Ltd (Mondaq). Mondaq grants you a non-exclusive, revocable licence to access the Website and associated services, such as the Mondaq News Alerts (Services), subject to and in consideration of your compliance with the following terms and conditions of use (Terms). Your use of the Website and/or Services constitutes your agreement to the Terms. Mondaq may terminate your use of the Website and Services if you are in breach of these Terms or if Mondaq decides to terminate the licence granted hereunder for any reason whatsoever.

Use of

To Use you must be: eighteen (18) years old or over; legally capable of entering into binding contracts; and not in any way prohibited by the applicable law to enter into these Terms in the jurisdiction which you are currently located.

You may use the Website as an unregistered user, however, you are required to register as a user if you wish to read the full text of the Content or to receive the Services.

You may not modify, publish, transmit, transfer or sell, reproduce, create derivative works from, distribute, perform, link, display, or in any way exploit any of the Content, in whole or in part, except as expressly permitted in these Terms or with the prior written consent of Mondaq. You may not use electronic or other means to extract details or information from the Content. Nor shall you extract information about users or Contributors in order to offer them any services or products.

In your use of the Website and/or Services you shall: comply with all applicable laws, regulations, directives and legislations which apply to your Use of the Website and/or Services in whatever country you are physically located including without limitation any and all consumer law, export control laws and regulations; provide to us true, correct and accurate information and promptly inform us in the event that any information that you have provided to us changes or becomes inaccurate; notify Mondaq immediately of any circumstances where you have reason to believe that any Intellectual Property Rights or any other rights of any third party may have been infringed; co-operate with reasonable security or other checks or requests for information made by Mondaq from time to time; and at all times be fully liable for the breach of any of these Terms by a third party using your login details to access the Website and/or Services

however, you shall not: do anything likely to impair, interfere with or damage or cause harm or distress to any persons, or the network; do anything that will infringe any Intellectual Property Rights or other rights of Mondaq or any third party; or use the Website, Services and/or Content otherwise than in accordance with these Terms; use any trade marks or service marks of Mondaq or the Contributors, or do anything which may be seen to take unfair advantage of the reputation and goodwill of Mondaq or the Contributors, or the Website, Services and/or Content.

Mondaq reserves the right, in its sole discretion, to take any action that it deems necessary and appropriate in the event it considers that there is a breach or threatened breach of the Terms.

Mondaq’s Rights and Obligations

Unless otherwise expressly set out to the contrary, nothing in these Terms shall serve to transfer from Mondaq to you, any Intellectual Property Rights owned by and/or licensed to Mondaq and all rights, title and interest in and to such Intellectual Property Rights will remain exclusively with Mondaq and/or its licensors.

Mondaq shall use its reasonable endeavours to make the Website and Services available to you at all times, but we cannot guarantee an uninterrupted and fault free service.

Mondaq reserves the right to make changes to the services and/or the Website or part thereof, from time to time, and we may add, remove, modify and/or vary any elements of features and functionalities of the Website or the services.

Mondaq also reserves the right from time to time to monitor your Use of the Website and/or services.


The Content is general information only. It is not intended to constitute legal advice or seek to be the complete and comprehensive statement of the law, nor is it intended to address your specific requirements or provide advice on which reliance should be placed. Mondaq and/or its Contributors and other suppliers make no representations about the suitability of the information contained in the Content for any purpose. All Content provided "as is" without warranty of any kind. Mondaq and/or its Contributors and other suppliers hereby exclude and disclaim all representations, warranties or guarantees with regard to the Content, including all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement. To the maximum extent permitted by law, Mondaq expressly excludes all representations, warranties, obligations, and liabilities arising out of or in connection with all Content. In no event shall Mondaq and/or its respective suppliers be liable for any special, indirect or consequential damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortious action, arising out of or in connection with the use of the Content or performance of Mondaq’s Services.


Mondaq may alter or amend these Terms by amending them on the Website. By continuing to Use the Services and/or the Website after such amendment, you will be deemed to have accepted any amendment to these Terms.

These Terms shall be governed by and construed in accordance with the laws of England and Wales and you irrevocably submit to the exclusive jurisdiction of the courts of England and Wales to settle any dispute which may arise out of or in connection with these Terms. If you live outside the United Kingdom, English law shall apply only to the extent that English law shall not deprive you of any legal protection accorded in accordance with the law of the place where you are habitually resident ("Local Law"). In the event English law deprives you of any legal protection which is accorded to you under Local Law, then these terms shall be governed by Local Law and any dispute or claim arising out of or in connection with these Terms shall be subject to the non-exclusive jurisdiction of the courts where you are habitually resident.

You may print and keep a copy of these Terms, which form the entire agreement between you and Mondaq and supersede any other communications or advertising in respect of the Service and/or the Website.

No delay in exercising or non-exercise by you and/or Mondaq of any of its rights under or in connection with these Terms shall operate as a waiver or release of each of your or Mondaq’s right. Rather, any such waiver or release must be specifically granted in writing signed by the party granting it.

If any part of these Terms is held unenforceable, that part shall be enforced to the maximum extent permissible so as to give effect to the intent of the parties, and the Terms shall continue in full force and effect.

Mondaq shall not incur any liability to you on account of any loss or damage resulting from any delay or failure to perform all or any part of these Terms if such delay or failure is caused, in whole or in part, by events, occurrences, or causes beyond the control of Mondaq. Such events, occurrences or causes will include, without limitation, acts of God, strikes, lockouts, server and network failure, riots, acts of war, earthquakes, fire and explosions.

By clicking Register you state you have read and agree to our Terms and Conditions