Hi,

The licensing sytem would have to very robust, in much the same way as say, medical practitioners or commercial pilots. They've even recently outlawed unqualified electricians.
At present anyone in the UK can repair safety critical equipment on vehicles with no requirement at all to demonstrate formal competence, which is plain wrong. For those with no formal qualifications, take some exams, if they know what they are doing, they'll pass them.
I wouldn't worry too much about it, because it will never happen.

Tom W