Is this
the cable ?
It's not as simple as that !
Since it's thermosetting, I assume table 4E2A would apply, and that does indeed say the cable is rated at 58A (6mm2 and clipped direct). But you have to read the notes, and in particular :
"1. Where it is intended to connect the cables in this table to equipment or accessories designed to operate at a temperature lower than the maximum operating temperature of the cable, the cables should be rated at the maximum operating temperature of the equipment or accessory (see Regulation 512.1.5)."
The EV point may or may not be so rated, but your CU and MCB almost certainly won't be. Therefore you need to downrate the cable - which means it'll actually only be rated the same as a thermoplastic cable to 70˚C (table 4D2A) where you'll find 6mm2 is rated to 46A.
Based on the above, I think the EV guy is right. But regardless, the EICR guy is wrong, absolutely no doubt just plain wrong and will now find himself paying for that.
Did he provide you with a certificate for that work ? If not demand one from him - if he is a member of one of the registration schemes (e.g. NICEIC) then I believe their rules make compliance with BS7671 mandatory. BS7671 says a certificate should be provided for any works.
Of course, to provide that he'll need to sign that the work he did complied with BS7671 - at which point he's guilty of fraud.
But regardless of whether you get a certificate from him, tell him he's coming back and a) replacing the MCB he took out, and b) replacing the front cover he vandalised to make a different one fit. As previously mentioned, BS7671 is clear that in a domestic environment, the CU must be a type approved assembly - which in practice means only using parts approved by that manufacturer for use in that board. To the best of my knowledge, no manufacturer certified a different manufacturer's breakers for "mix-n-match" in their boards.
"421.1.201 Within domestic (household) premises, consumer units and similar switchgear assemblies shall comply with BS EN 61439-3 and ..."
You may get "some resistance" from him, but your EICR guy is 100% in the wrong on fitting a different make/type of MCB. Regardless of whether there is a reason for downsizing the rating, the only acceptable action is fitting the correct breaker for the board. If he refuses to fix that, make it clear that you'll report him to both Trading Standards and his registration scheme for dangerous work.
As to whether it should be 32A or 40A, you can reasonably expect him to give a reason - it will be interesting to see what he comes up with. Bear in mind, we haven't seen the installation so are assuming (based on the description) installation method C "clipped direct" - it is possible that a different method may apply, but I think that's unlikely from your description.
Appendix 4 Section 2.4 gives the derating factor for stranded conductors as 0.95, so the rating of 46A from table 4D2A needs reducing to 43.7A. There's no derating for an MCB (there is for a fuse), so as 43.7 is higher than 40, that circuit would appear to be correctly designed.