The employer has requested we supply EVM data including ACWP & CPI. As it is our responsibility to carry out the work at the agreed prices are we required to supply this data?
No obligation for you to do so unless it is a specific requirement within the Works Information. You can share it if you wish to (and for relationship purposes you may choose to anyway) but not obligated. You have said they have requested - if they actually formally instructed you to do this, this would be a compensation event that at least you could seek recovery for with regards extra cost you would incur to do that that you would not otherwise have done yourself. Being option A, it does beg the question if it proves you are running late anyway from an EV (earned value) perspective what can they do about that anyway - as it will be your risk if you end up over running.
Having said all that, if you are going to do it anyway and not much hassle you could choose to just to show willing and show that you believe you are on schedule to deliver the works - it might help them to be able to accept your programme for example.
Just to add to Glenn’s answer, it looks like the Client is trying to get an indication of what your actual cost is, even though the contract was let under a main Option A, so unless the Scope requires this information you are not obliged to provide it. My guess is that they require this information for their internal reporting requirements. but that isn’t your responsibility.