What would my american boyfriend need in order to work as and electrician in the UK ?

He has been an electrician for 20 years in the USA but never took any exams for it, purely trained on the job. We are getting married so he will have a visa but i'm just wondering if he needs to take exams in the UK to work here as an electrician as i have heard we are alot more strict with saftey rules over here than they are over there.