Please do not ask me where to get a replacement licence as I don't know the answer! Try the company that trained you or the company you worked for at the time.

This quote is from the HSE web site

"There is no state system for training of lift truck operators as there is for drivers on the public highway. There is therefore no central organisation which holds copies of training certificates. To obtain a duplicate of your certificate of basic training you will need to contact the training provider who trained you and issued the original, or your previous employer, or the body which accredited the training."