Under the UK Construction Act payment regime, a paying party that intends to pay less than the sum notified must issue a valid pay less notice within the contractual deadline, setting out the sum it considers due and the basis of its calculation.
Miss the notice, or issue a defective one, and the notified sum becomes payable regardless of the merits: the foundation of smash-and-grab adjudications.
The word to sit with is regardless. If the notice is late or invalid, the notified sum becomes due even where the paying party has a strong case that the work was never worth that much. The merits do not rescue a missed deadline. This is deliberate: the payment regime exists to keep cash moving down the supply chain rather than to arrive at a perfect valuation every month.
A pay less notice generally has to do three things to be valid. It must be served within the contractual window, which is defined by reference to the final date for payment and is often shorter than people assume. It must state the sum the paying party considers due, not merely dispute the application. And it must set out the basis on which that sum is calculated, in enough detail that the other side can understand the deduction. A notice saying only "we disagree with your valuation" is unlikely to survive.
Service is where otherwise competent notices fail. Contracts specify who a notice goes to and by what method, and an email to a project manager when the contract names a different recipient can be fatal. Keep evidence of what was sent, to whom, by what route and when. A saved copy of a notice is not proof of service.
The regime rewards administrative discipline on both sides: applications and notices that are on time, properly calculated and properly served, with records to prove service. Underneath the paperwork sits the same question every valuation argument turns on, which is what was actually done on site in the period. A contractor who can evidence that day by day is in a different position from one relying on a monthly summary written from memory.
Behind every valuation argument is a question of what was actually done in the period; Construction Metric keeps that daily evidence without anyone writing it up: see how it works.