A verbal instruction on a construction site is given for a good reason almost every time. A detail does not work, the trade is on site now, and waiting for a formal instruction means standing them down. Somebody makes a decision and the work proceeds.
The cost arrives later, and it usually arrives twice: once as an argument about whether the work was instructed at all, and once as an argument about what it was worth.
What the contract usually says
Standard forms require instructions to be issued in writing by a named person. That requirement exists to make the record unambiguous, and it also limits who can commit the client to expenditure.
Most forms then provide a mechanism for verbal instructions: the contractor confirms in writing, and if the client or contract administrator does not dissent within a stated period, the instruction takes effect. The exact wording varies and amendments frequently change it.
Two things follow. First, a verbal instruction is not automatically worthless. Second, it only becomes effective if the contractor uses the mechanism, and the period for doing so is short.
Who can actually instruct
The contract names the person or role entitled to issue instructions. Advice from a design team member on site, an opinion from a client representative, or an agreement between two site managers is not an instruction, however senior the people involved.
This causes genuine confusion because the person giving the direction often does not realise they lack authority, and the person receiving it has no reason to doubt them. Work proceeds on the strength of a conversation that the contract does not recognise.
Making the position explicit at the start of a job takes ten minutes at a pre start meeting and prevents a category of argument entirely.
The evidence problem
Where no confirmation exists, the question becomes whether the work was instructed, and that is decided on whatever record survives. Site diaries, minutes, emails, photographs, delivery tickets and the sequence of drawing revisions all bear on it.
Records made at the time carry weight. Recollections do not, and they degrade quickly. Two people who were both present will often remember the same conversation differently and both be sincere.
This is why the practical answer is procedural rather than legal. The cost of confirming everything in writing is a few minutes a day. The cost of not doing it is measured in the final account.
Prime residential makes it worse
On a private residential scheme the client is frequently on site, has strong views, and gives direction directly to trades. That is natural and it produces exactly this problem at scale.
The answer is not to formalise the client out of their own project. It is to price every request quickly, in plain language, and put it in front of them the same day. Clients on these schemes are rarely trying to avoid cost; they want to know what a decision costs before taking it.
Where that habit is in place the final account holds no surprises, because each item was approved when it arose. The wider pattern is set out under prime residential.
Confirmation is not agreement
A confirmation of a verbal instruction records that an instruction was given. It does not agree what the work is worth, and it should say so.
The same distinction applies to signed daywork sheets and signed records of resource. Signing that four operatives were present for a day is a record of fact. It is not acceptance that four operatives were reasonably required or that the work should be valued on that basis.
Where signatures are given without that distinction stated, they are routinely presented later as agreement. Adding a short line to the effect that the signature records resource only removes the argument.
The habit that solves it
Every instruction confirmed in writing on the day it is given, by whoever received it, to whoever gave it, copied to the commercial team. No assessment of value, no argument, just a record.
Then each confirmed instruction valued in the following monthly valuation, or carried with a stated reason if it cannot be. An item that stays unvalued for three months is an item that will be argued about.
It is the least sophisticated cost control measure available and it removes more disputed value than anything clever. Where it has not been done, the effect compounds, and the pattern is set out in late design changes.
What this means for you
Establish at the pre start meeting who may issue instructions and how verbal ones are confirmed. Write it down and circulate it.
Then check monthly that the number of confirmed instructions roughly matches the number of things that have actually changed. A project with visible change and no confirmations is accumulating a problem that will surface at the final account. Monthly discipline on this sits under cost control and variations.
Have work on site that nobody instructed properly?
Send what records exist. We will tell you what position they support before anybody takes one.