I hate to put the cat among the pidgeons here but I think you will find that it is law that you should have training to operate any type of machine and also should be re-trained after an a given period of time (which is never stated).
I believe this crap is taken from the Management of Health & Safety Welfare Regulations 1999
I dont doubt what you say Jeremy, but this licence thing started back in the mid eighties, at first it was the plant hire companies that were to finance the licence to operators that had been working for them for X amount of years, and the companies would get some of the money back ...but then it snowballed from there to what it is now and it just getting silly now