I presume you are looking for training for a Counterbalance truck capable of lifting 45 tonnes+.
You would need to source a Training Company that can train operatives on B3 class of counterbalance trucks. Best way would look on the Governing Bodies websites (ITTSAR, RTITB, AITT) and look for training courses there.
However, you may face difficulties in getting training at a Training Centre because I doubt that many of them will have access to a B3 class truck unless they can hire one in specifically and even then it is also having the area available to operate the truck, so unless you are working for a company who use lift trucks that deal with the weights you are asking about, the question is why do you need the training? And there is no such thing as a Fork Lift Licence in the UK :)