NEC TSC Option C - PM's assessment of a comp event

We are in a TSC option C contract and have been asked to submit a quotation for a proposed instruction. We completed our tender of the proposed instruction at circa £50k, but the Service Manager has now made an assessment and implemented the instruction at a value of £25k through the BIM platform we are using. Is he allowed to instruct a proposed instruction based on his own assessment?
Thanks in advance.

You have not said if the TSC is NEC3 or NEC4, this is really important as the answer is different in each case.

In NEC3 TSC the SM can instruct you to submit a quotation for a proposed instruction under clause 61.2 and the quotation follows the normal CE procedure of revise / accept / assess or not give proposed instruction.

However in NEC4 TSC the SM has limited powers, they can still instruct a quotation under clause 65.1 but this time the reply is either revise / instruct and accept / not accept, the powers to assess have been removed.

Your next move again will depend, in NEC3 TSC if the quotation has been assessed and implemented your only recourse is adjudication, and in NEC4 TSC you could use the Senior Representatives procedure before adjudication.

Interestingly the NEC3 TSC is silent about how the proposed instruction becomes an actual instruction, presumably the SM just issues the instruction under the relevant clause of the contract. NEC4 TSC covers this point at clause 65.2. Once the instruction is issued it is binding on the Contractor under clause 27.3 (NEC3) or clause 25.3 (NEC4) so the Contractor cannot use its dissatisfaction with the commercial outcome as a reason not to do the work.

Thanks for this Neil, really helped me out.