There are four options:
1) Rip out and replace.
2) De-rate the CPD.
3) Disconnect and leave alone.
4) Leave as is and do nothing.
You've already stated that ripping out and replacing is not an option.
It's been pointed out to you what the maximum rating of CPD should be if you de-rated, but you appear to be having trouble understanding the reasons.
That leaves you with disconnection or leaving as is.
Just to set your mind at rest, as has already been pointed out by others, there is nothing in the Regulations prohibiting the use of flex for fixed wiring.
The only reason (from the information you have provided) that the situation doesn't comply is that the CPD is rated too high for the conductors used.