My original question relates to an Employer designed scheme under NEC 3 Option A and specifically to the situation where the Contractor’s proposal is more expensive than the original design.
Unusual to be suggesting a more expensive proposal, but I can see that could happen. This would require an instruction from the Project Manager which would normally not be a compensation event as it is normally notified for your convenience, but if this will be more expensive then you need to get this agreed that it will be a CE otherwise you will not get recovery.