Unless you have UK CAA LWTR or an acceptable apprenticeship, you will have to provide the FAA with proof of 18 months airframe training, and 18 months powerplant training. Usually they are done concurrently, but it takes about 2 years by the time you factor in the exams - as Jet Fixer has intimated. There is a practical ( hands-on ) plus an oral exam after you have passed the written exams. I don't think there's anybody in the UK that provides the required technical training, and unless times have changed, you'll have to go to Frankfurt to take the exams with the FAA. Your best bet is to apply for a student visa ( good luck ) and come to the US for 2 years to do it here. Your better bet is forget it and spend your time on flying them not fixing them.