This article is from the website of a company which provides forklift training courses:
http://www.fork-lift-training.co.uk/news_items/forklift-licence.html
It appears to confirm my own understanding that, in the UK, there is officially NO transferable qualification in driving forklift trucks and that all qualifications are valid 'in house' only.
However that does seem at variance with the courses provided by local probation services, who often help ex-offenders get some type of forklift qualification in order to help them seek employment.
Even so, if you did your training entirely 'in house' with Employer A, then any certificate issued by them won't be valid elsewhere anyway. (i.e. if you could get hold of the certificate and give it to Employer B, and you then had an accident while using a forklift truck with Employer B, Employer B could be prosecuted by the Health & safety Executive for failing to provide you with their
own training).