HOVERJOCKI
I suggest you download a copy of
LASORS from the CAA site which attempts to explain the licensing requirements. You will probably want to start in Section D4.5 page 24.
Essentially, you will need to sit 13 written exams if you want theory credits for an ATPL, or 9 for a CPL. It will then be 'training as required' by the Head of Training of the school you decide to train with followed by a flight test. You will also need a JAA medical.
VeeAny
I'm not sure that would work for an FAA licence as they do not have type ratings for smaller types. Therefore, the CAA would probably have a restrictive reading of this:
F9.1 TRANSFER OF TYPE/CLASS RATINGS FROM A NON-JAA STATE LICENCE
Type Ratings
(Aeroplane/Helicopter)
A type rating endorsement on a licence issued by a non-JAA State may be transferred to a UK issued pilot’s licence, subject to:-
i. 500 hours flying experience as pilot on type, operating as P1 or P2 appropriate to the rating required (PUT time may not be counted).
ii. Operational experience as pilot on type within the preceding 5 years.
iii. Pass a Proficiency Check on type with a JAA Authorised Examiner.
iv. Have met the requirements of JAR-FCL 1.250/2.250, 1.251 and 2.255 as applicable, including knowledge of aeroplane performance appropriate to that type (please refer to Section F4 - Knowledge of Aeroplane Performance).