Rock Advertising made NOM clauses effective

Rock Advertising Ltd v MWB Business Exchange Centres Ltd [2018] UKSC 24 settled a previously unstable area. The Supreme Court, with Lord Sumption leading, held that a contractual term requiring variations to be in writing is fully effective, and overruled the contrary obiter reasoning in Globe Motors Inc v TRW Lucas Varity Electric Steering Ltd [2016] EWCA Civ 396. The rationale is party autonomy: parties who agree a formal channel for variations are entitled to certainty that informal channels will not bind them.

Lord Sumption identified three commercial purposes of NOM clauses - preventing attempts to undermine the written terms, avoiding disputes about whether and on what terms a variation was agreed, and helping a corporation control the authority of its personnel to bind it. The clause is now firmly embedded in English law.

The estoppel exception is narrow

The exception Lord Sumption preserved is deliberately limited. A party relying on an oral variation must show (i) words or conduct unequivocally representing that the variation is valid despite informality, and (ii) 'something more' than the informal promise itself. Mere performance of the alleged variation does not satisfy the test.

The Supreme Court applied the same restrictive approach in Kabab-Ji SAL v Kout Food Group [2021] UKSC 48: a company that had not signed an amendment could not be bound into the contract (and its arbitration agreement) through course of performance, because the no-oral-modification requirement had not been met. Preserving the estoppel expressly in the clause does not widen it, but it removes the argument that the parties contracted out of any estoppel exception altogether.

The electronic-signature trap and waiver by conduct

The dominant modern source of NOM disputes is electronic execution. A clause that requires variations to be 'in writing and signed' but says nothing about electronic signatures invites argument over whether an emailed PDF, a DocuSign or an Adobe e-signature satisfies it. The fix is to define 'in writing' and 'signed' to include recognised electronic-signature methods that produce an audit trail.

The clause should also exclude waiver of the NOM by conduct. Without that, the very conduct said to constitute an oral variation can be re-cast as a waiver of the NOM clause itself - which defeats the purpose. A short provision stating that the NOM can only be waived in writing closes the loop.

The cross-border angle

This is the boilerplate clause with the most acute civil-law tension. Where the UN Convention on Contracts for the International Sale of Goods applies and has not been excluded, Article 29(2) validates NOM clauses but precludes reliance on them where the other party has acted on conduct inconsistent with the clause - materially wider than the Rock Advertising estoppel. In Germany, section 125 of the BGB makes form-defective transactions void, but the good-faith principle in section 242 can override where the parties have lived under the varied terms. French law (Articles 1104 and 1188 of the Code civil) can give effect to oral variations notwithstanding a NOM where reliance is established.

Other systems differ again: under Russian law the consequence of breaching a simple written-form requirement is often limited to restrictions on witness evidence rather than invalidity (Civil Code Article 162), with variations generally required to follow the form of the original (Article 452); and the UAE's reformed Civil Transactions Law (Federal Decree-Law 25/2025) reinforces good faith and abuse-of-rights constraints that can limit a formalistic NOM defence where reliance has been induced. The lesson is that a NOM clause that is decisive in London may be far weaker in the enforcement forum, and the cross-border drafting has to take that into account. The Singapore Court of Appeal, for instance, declined to follow Rock Advertising in Charles Lim Teng Siang v Hong Choon Hau [2021] SGCA 43, treating a NOM clause as raising only a rebuttable presumption.

Use at the desk

Practical checklist

  • Use a NOM clause where certainty about variations matters - it is fully effective under English law (Rock Advertising).
  • Define 'in writing' and 'signed' to include recognised electronic-signature methods that produce an audit trail.
  • Exclude waiver of the NOM clause by conduct; require any waiver of it to be in writing.
  • Preserve the Rock Advertising estoppel expressly - it does not widen the exception but removes a contracting-out argument.
  • Remember mere performance of an alleged oral variation does not engage the estoppel (need 'something more').
  • In a cross-border deal, check the CISG and the forum's good-faith rules before relying on the NOM (it may be weaker abroad).

This guide is informational only and is not legal advice. It does not replace advice from licensed counsel on the facts of a specific transaction.

Product demo

Use the guide for context. Use Veqtor for the Word documents.

Watch Claude compare negotiation drafts and create a separate Word document with proposed tracked changes.

See Veqtor work with Word redlines

Continue reading

Pillar guideBoilerplate clausesBoilerplate clauses

How the boilerplate clauses - entire agreement, NOM, notices, waiver, severability and third-party rights - actually operate under English law, and what changes in a cross-border deal.

5 min readWaiverBoilerplate clausesNo-waiver clauses and election

Why a no-waiver clause is not absolute - election, the distinction from estoppel, Tele2 on affirmation, and the reservation-of-rights letter.

4 min readContract interpretationDefinitions and recitalsHow do courts interpret contracts?

The Wood v Capita framework, Lord Hodge's principles, and how textual and contextual analysis decide meaning.

4 min readCross-borderBoilerplate clausesEnglish law as the only connection

When English law is the only connection, the boilerplate must survive the enforcement forum - Rome I Articles 3, 9 and 21, the purely-domestic carve-out, and New York Convention Article V(2)(b).

5 min read