Advising clients on the best approach to managing commercial contracts means engaging with the daily tension clients face: the need to be responsive and agile when managing live contracts on the ground, while maintaining clear documentation and adhering to formal change control procedures. For public sector bodies, this tension is heightened by the dual demands of rigorous governance and transparency.
That tension, left unmanaged, creates what those advising in this area call "drift" — and drift can prove enormously costly when supplier performance deteriorates and enforcement becomes necessary.
The reality of day-to-day contract management
No contract, however carefully drafted, perfectly anticipates every operational development. Requirements evolve, personnel change, and commercial pressures demand swift decisions. In the public sector, this challenge is amplified by the need to operate within standing orders, rules of delegation, and public procurement rules.
A client organisation may be tempted to "sort it out informally" — and that temptation is entirely understandable. A supplier misses a delivery deadline; an urgent workaround is agreed verbally on a project call. Additional scope creeps in at the request of an end-user team without a formal change request. Performance benchmarks are quietly adjusted to reflect "how things actually work" rather than what the contract requires. Over time, a series of small informal accommodations can mean the live commercial relationship bears little resemblance to the signed contract. The danger becomes acute when a party eventually seeks to enforce the contract as written. At that point, the gap between contractual obligation and operational reality can fundamentally undermine the enforcing party's position — both legally and commercially.
Formality matters: The "No oral modification" clause
Many commercial contracts contain "no oral modification" (NOM) clauses, requiring any variation to be made in writing and signed by authorised representatives. These provisions are routinely treated as standard boilerplate, their significance underestimated by those managing contracts day to day. When advising a client who has been operating under informal arrangements, the presence or absence of a NOM clause should be the first port of call.
The importance of such clauses was confirmed decisively by the Supreme Court in Rock Advertising Ltd v MWB Business Exchange Centres Ltd [2018] UKSC 24. The Supreme Court held unequivocally that NOM clauses are legally effective: an oral agreement to vary the contract, even one genuinely reached and acted upon in good faith, will not be binding where the contract requires written agreement. The Court rejected the argument that a subsequent oral agreement could itself waive the NOM clause.
Practitioners should note, however, that Lord Sumption expressly left open whether estoppel could in some circumstances prevent a party from relying on a NOM clause. Where a client has acted to its detriment in reliance on an oral variation, an estoppel argument may still arise on the facts.
The practical message is stark. Informal arrangements — however commercially sensible and however strongly both parties believe they have reached a binding understanding — may carry no legal weight. Where a NOM clause exists, any commercially meaningful accommodation must be documented and formally executed. Where a client has already entered into informal arrangements, the priority should be to assess urgently whether those arrangements can be ratified through a properly executed written variation before any dispute crystallises. Practitioners should also check whether the individuals who agreed any informal arrangement had actual or ostensible authority to bind their organisation — an arrangement agreed without proper delegated authority may not bind the client but may equally create exposure on estoppel grounds if acted upon.
The entire agreement clause
The "entire agreement" boilerplate found in virtually all well-drafted commercial contracts provides that the written contract constitutes the complete and exclusive agreement between the parties, superseding all prior negotiations, representations, and understandings. Where a contracting party has relied upon assurances given during negotiations — or upon side-letters, emails, or meeting notes supplementing the formal documentation — an entire agreement clause can extinguish any legal reliance upon them. Courts have consistently upheld such clauses: see Inntrepreneur Pub Co Ltd v East Crown Ltd [2000] 2 Lloyd's Rep 611, where Lightman J confirmed that a properly drafted entire agreement clause will preclude reliance upon pre-contractual representations, even where those representations have influenced the other party's decision to contract.
Practitioners should qualify that analysis in two important respects. First, entire agreement clauses do not automatically exclude liability for fraudulent or negligent misrepresentation. Any non-reliance wording purporting to exclude misrepresentation liability must satisfy the reasonableness test under section 11 of the Unfair Contract Terms Act 1977: see Springwell Navigation Corporation v JP Morgan Chase Bank [2010] EWCA Civ 1221. Second, where a client has given pre-contractual assurances to the other side — rather than received them — this analysis runs in reverse and may expose the client to a misrepresentation claim that the entire agreement clause does not cure. Where pre-contractual assurances or supplemental understandings have commercial significance, the correct approach is to ensure they are incorporated into the contract itself.
Waiver: The risk of losing rights through inaction
Perhaps the greatest risk associated with drift is waiver. The law recognises two distinct but related mechanisms by which rights can be lost through inaction or acquiescence.
First, at common law, a party that — with knowledge of a breach — elects to affirm the contract rather than terminate may lose the right of termination permanently: see Peyman v Lanjani [1985] Ch 457. Election requires full knowledge of the relevant facts and of the legal right being exercised, but once made, it is irrevocable. A contract manager who continues to pay invoices, accept deliveries, or otherwise treat the contract as subsisting following a repudiatory breach may be taken to have elected to affirm, permanently extinguishing the right to terminate on that ground. A practitioner should confront that risk directly and advise on the scope of any rights that may have been lost before any enforcement strategy is developed.
Second, the equitable doctrine of promissory estoppel — firmly established in Hughes v Metropolitan Railway Co [1877] 2 App Cas 439 — provides that a party who, by words or conduct, leads the other to believe it will not enforce its strict contractual rights may be precluded from later doing so without first giving reasonable notice. In practice, where poor performance has been repeatedly tolerated without formal objection over a sustained period, a counterparty may argue persuasively that rights to terminate have been suspended and that reasonable notice is required before strict enforcement can recommence.
When advising, it is important to be clear with the client on the scope and limits of promissory estoppel. In English law, promissory estoppel is generally a shield, not a sword: it does not create a free-standing cause of action but may operate to prevent a party from enforcing strict legal rights. Mere passive tolerance, silence, or delay will not ordinarily found an estoppel; the court will look for a clear and unequivocal representation (by words or conduct), reliance or change of position, and circumstances making it inequitable to resile. Courts are slow to infer the surrender of valuable rights from inaction or ambiguity, but a sufficiently clear course of dealings can, in the right case, give rise to real estoppel risk.
The cumulative effect of these doctrines means that inaction is never truly neutral. A client who has allowed underperformance to continue without formal complaint may find themselves significantly constrained when they eventually seek to act.
Contractual relief mechanisms: Use them or lose them
A further and often overlooked manifestation of drift arises where parties fail to comply with the contractual machinery governing relief events, delay claims, extensions of time, service credits, or other contractual protections. These provisions are frequently viewed by operational teams as administrative formalities. In reality, they often form a fundamental part of the contract's risk allocation framework and can determine whether a party is entitled to rely on a particular defence or excuse for non-performance.
The importance of adhering to contractual relief procedures was illustrated in CIS General Insurance Ltd (Co-op) v IBM United Kingdom Ltd [2021] EWHC 347 (TCC). The court reinforced the principle that where sophisticated commercial parties have agreed a particular process for obtaining contractual relief, the court will generally expect that process to be complied with. A party that fails to invoke the agreed mechanism or satisfy the contractual preconditions for relief may find itself unable to rely upon matters that might otherwise excuse delay or underperformance.
Suppliers should ensure that relief events, dependency failures, and extension requests are raised strictly in accordance with the contract. Customers should be wary of routinely accepting departures from contractual notice and escalation procedures. A consistent failure to follow the agreed contractual machinery can significantly weaken a party's position when a dispute eventually arises.
When the informal arrangement begins to break down
The first priority is to audit the gap between the signed contract and operational reality. This involves a systematic review of correspondence, meeting minutes, change records, and invoicing history. Emails, WhatsApp and Teams messages, call records, and informal meeting notes can all be relevant, and the client should be advised to preserve all such materials — including those held on personal devices — before any review of electronic communications takes place.
Where the client wishes to revert to strict contractual enforcement, this should not be done abruptly. As the House of Lords confirmed in Tool Metal Manufacturing Co Ltd v Tungsten Electric Co Ltd [1955] 1 WLR 761, rights suspended by estoppel can generally be revived on reasonable notice because promissory estoppel does not permanently extinguish the underlying right but merely suspends it. Notices should be drafted carefully to expressly reserve existing contractual rights, make clear that no waiver is intended by past conduct, and put the supplier formally on notice of the specific obligations it must meet going forward.
Where informal variations have been acted upon by the supplier to its detriment, estoppel may go further than merely suspending rights, and clients may face arguments that the variation has become binding in substance. Advice specific to the facts will be essential before any enforcement steps are taken.
Checklist for Practitioners
The key priority when advising any contracting party is to consider whether day-to-day contract management undermines its legal and commercial position. Practitioners should consider whether the following disciplines are maintained:
Change control and conformed contract maintenance. Does the client process all variations through formal change control and update the conformed contract accordingly?
Governance and delegation. Apply governance processes and delegation authorities consistently, ensuring those approving changes have the authority to do so. An adviser should check not only whether a variation is in writing, but whether the individuals who agreed it had actual or ostensible authority to bind their organisation.
Ratification of informal variations. Contract variations already agreed informally should be ratified through a properly executed written instrument as a priority.
Contractual notice, escalation, and relief procedures. Has the client followed these rigorously? Contractual machinery is often the gateway to contractual protections, and failure to follow it can result in valuable rights being lost.
Reservation of rights. Where the client is allowing time for performance to improve, it should expressly reserve its rights, making clear in unambiguous terms that no waiver is intended and that all contractual remedies remain available. Reservation provisions should be clear and prominent — not buried away in routine correspondence.
Regular contract reviews and entire agreement discipline. Clients should conduct regular reviews to identify and correct drift before it becomes entrenched. The entire agreement clause should be treated as a discipline: if something matters commercially, it must be captured within the contract itself.
- Early instruction. The sooner a legal adviser can assess the position, the greater the range of options available should things go wrong. Clients should not wait for a formal dispute to crystallise before seeking advice on informal arrangements that have already developed.
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