Jacko 130
You won't be starting from scratch as you will have a lot of the flying hours already (cross country etc).
You will need to sit the exams and that is your biggest challenge
You may get exemptions from the CAA (BUT DONT HOLD YOUR BREATH ON THAT).
Suggest you order the distance learning pack from somewhere like Bristol GS and get cracking on the theory. Second thing that you can do is send your logbook and copy of licenses to CAA and ask them for an assessment of experience against requirements for JAR license (it will cost a fee but they will then advise you what YOU need to do).