Why variations go unpaid, and why the leak lands hardest on specialist subcontractors

Published 3 October 2026 · VariationFlow

Why variations go unpaid on UK construction jobs, explained for specialist subcontractors: an illustrative anatomy of a lost variation under the NEC4 subcontract’s clause 61.3 time bar, the five process failures behind the loss, what research by FIS and the University of Reading shows about the sector, and why insolvency and late payment make it matter more than ever.

Nobody decides to write off a variation. It slips. What follows is an illustrative example rather than a real job, and its figure is invented for the purpose, but nothing in it is unusual.

The anatomy of a lost variation

1. Monday, 7.42am. The supervisor is asked, on site and out loud, to reroute a drainage run, takes a photograph on a personal phone and gets the team started. Nothing is written down, because there is a programme to hit. £18,400 of work is now at risk.
2. That week. The job gets busy and the change is never written up. The photograph sinks into a camera roll of two thousand others. Everyone assumes someone else has logged it.
3. Six weeks later. At the monthly valuation the QS spots the extra work. There is no written instruction, no dated notice and no evidence pack: a memory, and one photograph nobody can find.
4. Week nine. The job is on the NEC4 Engineering and Construction Subcontract. Nobody on either side notified the change as a compensation event, so the duty to notify it fell to the subcontractor under clause 61.3, within seven weeks of becoming aware of it (on the main contract the period is eight). That window has closed, and with it any change to the Prices or the Subcontract Completion Date. The bar is all or nothing: the work was real, and the claim is gone.
5. Final account. “We’ve no record of that.” The main contractor declines the item. With nothing made at the time to stand on, the subcontractor drops it, to protect the relationship or to settle the rest of the account. £18,400 is written off.

Nobody decided to lose £18,400. It slipped, a step at a time, and each step seemed reasonable when it was taken. The example is illustrative and its figures are invented; the clause 61.3 time bar it turns on is real. Repeated across every job and every month, losses like this one add up, and because the work was never recorded, no report shows where they went.

What does it mean for a variation to go unpaid?

A variation goes unpaid when work the contract would have paid for is done and the money never arrives, not because the claim failed on its merits but because it was never recorded, never submitted, submitted too late, or could not be proved when it was challenged. Some of it is lost to a contractual time bar, like the compensation event in the example. The rest is lost more quietly: discounted at the final account, traded away to close the account, or simply never asked for. We know of no published figure for the value of variations written off across UK construction, because it is not something anyone measures systematically, and that gap is part of the problem. A loss nobody counts is a loss nobody manages.

Why does it keep happening?

Revenue lost on variations is rarely one catastrophic failure. It is a slow bleed from small process failures, repeated on every project. Five come up again and again.

1. Evidence trapped on personal phones

Site photographs live on operatives’ own phones, voice notes in message threads, site instructions on a clipboard that goes missing. By the time a variation is disputed, months later, the evidence has gone with them. The party claiming the money has to prove it, under NEC4 and JCT alike, and without a record made at the time you are negotiating from nothing. Verbal instructions are the sharpest case of it.

2. Submissions made too late, or never

A firm that writes up its variations once a month, at the valuation, can take six weeks to submit a change made at the start of a month. On an NEC4 subcontract that can be fatal: a compensation event the Contractor has not notified must be notified within seven weeks of becoming aware of it, or the entitlement is lost (clause 61.3; eight weeks on the main contract, and often less where Z clauses shorten it). The guide to NEC4 compensation events sets out the whole procedure. On JCT forms, recovery of loss and expense turns on a notice given as soon as the effect on progress becomes reasonably apparent, and a late notice is the first thing the other side will point to.

3. No formal written submission

A variation raised in conversation, or in an email with no reference and no price, is commercially fragile. The main contractor can say it has no record of it. Without a dated, referenced submission, a valid claim becomes one person’s word against another’s, which is a weak position to take into an adjudication.

4. Commercial knowledge in one person’s head

Where the variation register is one QS’s spreadsheet, it is only as current as that person’s week. Annual leave, a new job or a delivery peak, and variations slip. By the time the register is looked at again, some are out of time and others have been forgotten.

5. Nobody chasing ageing submissions

A variation submitted on Monday is forgotten by Friday unless something brings it back. Without tracking, submissions sit unanswered for six, eight or twelve weeks. On the NEC4 subcontract that silence can work for you: if the Contractor does not reply to a quotation within the four weeks clause 62.3 allows, you can notify the failure, and if the silence runs on for a further three weeks the quotation is treated as accepted (clause 62.6). That only helps someone who is counting. More often an unanswered submission simply loses its leverage as the job moves on.

Why does the leak land hardest on specialist subcontractors?

Subcontractors sit at the bottom of the payment chain. They buy materials and pay labour weeks before their first payment application, then absorb late certification, slow payment and retention. When a variation is not watertight, revenue already earned becomes a write-off, or a discount used against them at the final account. Research by FIS and the University of Reading, published in February 2023, shows how routine the pressure is. Of the specialist subcontractors who answered:

• 70 per cent said the final account exceeds the initial contract price because of changes in scope always or most of the time. Among main fit-out contractors the figure was 63 per cent.
• 65 per cent said that, having tendered formally for a package, they are asked to reduce the price retrospectively always or most of the time.
• 83 per cent at least sometimes start on site with no formally signed contract, which leaves the entitlement to variations fragile from the first day.

One respondent put it plainly: “At the end of a project, we are frequently asked to reduce our price as the Contractor cannot get more money from the Client. [This] is usually done based on not accepting variations.”

Source: FIS / University of Reading, “Procurement in the finishes, fit-out and interiors sector” (February 2023; 269 respondents).

Why does this matter more than ever?

Construction has the highest number of company insolvencies of any UK sector, around 17 per cent of all company failures. When a contractor above you collapses, your unrecovered variations and retention become unsecured debt you are unlikely ever to see. ISG’s collapse in 2024, the largest in the industry since Carillion, left debts of more than a billion pounds, and its unsecured creditors are not expected to recover anything. Late payment, on the government’s own estimate, costs the UK economy around £11bn a year. A variation recovered this month is cash; the same variation still being argued when the contractor above you fails is a line in a list of creditors.

Sources: Construction News (January 2026); Department for Business & Trade / Small Business Commissioner (2025); Insolvency Service (2024).

What closes the leak?

Every cause above is a gap between the moment a change happens on site and the moment it is recorded, and the answer to each is the same: a record made at the time, a date someone is watching, and evidence that can be produced on demand. That is what VariationFlow is built to do.

• On site, the VariationFlow app captures a change in about a minute: what changed, who asked for it and their signature, photos, a voice note and the location, with or without signal, in the crew’s own language.
• Variation management takes it from there: a submission to the main contractor with a review link they can answer without an account, a register the whole commercial team shares, submissions marked at 28 and 42 days, the NEC4 subcontract and JCT clocks on every variation, and an audit PDF and evidence pack for a dispute.
• The CVR sets value against cost on every project each period, with a value adjustment to carry a disputed variation below its claimed value, so the margin is seen before the final account rather than at it.
• QA Flow keeps your own quality record: inspections, NCRs, snags and hold points, signed off by the main contractor by link, which is the evidence to set against a defects deduction at the end of the job.
• For builders working directly for homeowners, Builder sends the quote online for the client to accept, has extras priced and agreed in writing, and invoices by stage.

This article is general information, not legal advice. Whether an event is a compensation event, which notices your contract requires and what its periods are all turn on the words of your own subcontract and any amendments to it, and are worth an adviser’s eye before a deadline is relied on.