a quick update.ive spoken with Napit on this subject, they took the stand that i couldn't sign the kitchen work off as i had not witnessed the wiring at first fix stage, however it was their view that realistically if i installed an rcd to the circuit and it passed all tests it would be deemed safe to energise the circuit and prove the work wasnt a danger, however my cert could only cover the rcd installation, all seems fair.
however since speaking to the customer further it would appear he has numourous complaints with this job and ive decided not to go ahead with the remedial works.
some jobs are just not worth it
thanks for the replys lads