It used to be easier to start as an apprentice, but nowadays employers usually prefer you to have an NVQ or other qualification before you start. I know Liverpool Community College has one, but if you go to learndirect.co.uk they can tell you more - about types of NVQ, which other centres in Liverpool offer them etc.

It's also worth approaching some local garages, especially a bigger employer like Qwikfit, and asking them what kind of qualifications they look for. Level 2 NVQ is often mentioned, but see what they say. Good luck.