Three moments, three regimes
| Moment of discovery | Who acts | Effect |
|---|---|---|
| Before tenders are submitted | the tenderer | report, possible corrigendum |
| During analysis of tenders | the contracting authority | verification and rectification |
| During execution | both | final account or additional work |
The first moment is the only one where the error costs almost nothing. A corrigendum published before submission lets all tenderers price the same thing, and equal treatment is preserved.
What the tenderer gains by reporting
Contract documents generally require the tenderer to report errors and gaps discovered in the documents, within a period before the submission deadline. Silence can later be held against them.
Beyond the duty, three practical reasons argue for reporting. They concern comparability of tenders, risk and the contractual relationship.
Silence does not pay on a provisional quantity. Under that regime payment follows quantities actually executed: speculating on an understated quantity gains nothing, since the excess will be due anyway at the rate offered.
Silence is risky on an omitted item. A contractor who spotted the omission and said nothing ends up negotiating additional work in a relationship where their position is weakened by the knowledge they had of it.
Reporting improves comparability. A tender built on a corrected bill compares better, which serves the contractor whose offer is genuinely competitive.
What the contracting authority does during analysis
The mechanism is set out in the article on measurement in public contracts, and two points bear repeating here. Time limits and forms are specified there.
It seeks the tenderer's real intention before questioning them, comparing the tender with others and with current prices.
It may decide that the unit rates apply where rectification is not otherwise possible. A tender whose total does not match its rates may therefore be recalculated on the basis of those rates.
Its liability is not engaged where it fails to detect an error. There is therefore no safety net for the careless tenderer.
During execution
This is the costliest moment, and allocation depends on the regime of the item. An error found during the works is no longer corrected free of charge.
Under a provisional quantity, the difference is settled at final account, at the agreed rate. The client bears the excess, the contractor keeps its price.
Under a lump-sum quantity, the difference stays with whoever the contract designates, without adjustment.
Where an item is absent, there is neither quantity nor price. The work becomes additional work, priced by negotiation without competition, which is structurally unfavourable to the client.
These regimes are set out in the article on provisional and lump-sum quantities. The allocation of risk is explained there regime by regime.
The designer's role
They are not party to the works contract, but they are not out of the picture. The bill author's liability is assessed on their own appointment.
A manifestly incomplete or inconsistent bill may engage their professional liability towards their client. That is precisely what the detailed measurement documents, covered in the article on summary and detailed measurement.
The useful distinction is between error and unforeseeability. A provisional quantity that turns out different at execution is not an error: that is how the regime works. An omitted item is one.
What this means for a professional
Four rules.
Report within the period provided, in writing and keeping proof of sending.
Do not build a pricing strategy on an error spotted. The hoped-for gain is uncertain and the exposure real.
Check consistency between rates and totals before submission, since the former may prevail.
Document assumptions on items whose quantity looks doubtful, so as to be able to discuss them usefully later.
This article reflects the position of the rules at the date of checking and serves professional orientation. It does not constitute legal advice and does not replace assessment of the individual case.