In addition to the LASORS entries, if you don't want to be paid for instructing, you don't need a CPL or a Class 1 Medical, but you DO need either to pass the CPL or ATPL exams or to have earned the D3.3 credit.
E.g., Ex-C130 pilot with 2000 TT, of which 1000 is PIC (C130) and 500 is PICU/S (e.g. co-pilot acting as Op Pilot) who is an ex-Bulldog A2 and wants to be an unpaid civvy FI - and who has never held a CAA licence before:
Pass CPL (or ATPL) Air Law
Pass Class 2 Medical
Complete the FI reqts as per LASORS
But, if you want to be paid:
Pass ATPL Air Law
Pass Class 1 Medical
Have a C-130 IR observed by a CAA IRE
Complete the FI reqts as per LASORS
There are a whole host of conditions applying if you are ex-FJ, not ex-ME or if you don't have 2000 hrs TT - my case above shows only the simplest.
You might try ELC to cover some of the costs?
Also, the only person I would berate would be someone who tells you to "Ask the CAA". Yes, it's all in LASORS, but don't bother the CAA until you've researched LASORS and find something you don't understand.
DownloadDog, if you can be more specific with your current totals (ish) and types, plus when you last practised the noble art of instructing and on what - and whether you've ever held a licence before, I could give you a more complete answer. Also the contact details for a flying training organisation which is very familiar with the ex-QFI brush-up requirements and is based near Stratford-upon-Avon.
SHT.....LAI....PAAT...00!!