This happens quite often.
The CAA will let you have a replacement copy but will charge you for it. I believe that the fee is £20 or £30.
FTOs are required to keep training records for 5 years. If you are lucky yours might still have them on file. If they have, they will probably give you a copy for free. An FTO would need to be very well organised to ensure that old records are destroyed after exactly five years, so you may be lucky.