You can go back to college and do a 2 year course at bristol or kingston if you want to be a B2 engineer(avionics) or if you want B1 (mechanical) then you could go to newcastle as well.
If you dont want to go back to college then Monarch do an adult training course, where you could re-train whilst being paid, but the wages are not that good and you would end up as a fitter not licensed.
Ideally if you want to be serious about a career as an aircraft engineer then you should be thinking about being licensed. Either way you will need 2-5 years practical hands on aircraft practise before you can apply for your license.
Any questions just pm me and ill be happy to answer where I can.