BCPLs may still be re-issued, even though the CAA reduced their validity period from 10 to 5 years with no Regulatory Impact Assessment....
I would suggest that you get your BCPL re-issued. Just fill out the appropriate forms indicating that you have a current Class 1 medical and SEP Class Rating and send it off to the CAA..........together with the appropriate fee.
There are quite a few people around who instruct for remuneration using a Restricted BCPL, let alone a full BCPL.
I am 99% sure that you will be OK to start a FI course (no such thing as an AFI course) with a UK BCPL - but check with a
good FTO first.
One thing - the UK yes-men on the EASA team seem to think that EASA will get rid of National licences in the next few years. This outrages me and I will be taking up the cudgels appropriately. The more BCPLs still in exitence, the more the CAA will have to sort out transition arrangements with the Eurocrats of Koln!