MLP: Here is what the CAA bible says on the subject of crediting hours on an uncompleted non-JAA (e.g. FAA) PPL(H) course towards the grant of a JAA PPL(H):
In circumstances where previous flying training
towards an ICAO PPL(H) (non-JAR-FCL) has
been completed but no licence has been issued,
PLD will consider the crediting of such flight time
towards the issue of a JAR-FCL PPL(H). In all
cases, applicants must apply in writing to PLD
enclosing appropriate training records and flying
logbooks for the PPL training received. PLD will
review the training records to establish a course
of training and advise the applicant accordingly.
(PLD = UK Civil Aviation Authority Personnel Licensing Department).
As to what hours are best to do, I'm not a heli instructor but these are the specific minimum requirements for the JAA PPL(H) (within the overall minimum 45 hours):
25 hours Dual Instruction on Helicopters, which must include 5 hours Instrument dual instruction;
10 hours Supervised solo flight time on Helicopters, which must include 5 hours Solo cross-country flight time, which must include one cross-country flight of at least 185km (100nm) during which full stop landings at two aerodromes different from the aerodrome of departure shall be made.
NB night flying is of no value to someone training for a JAA PPL(H) because you can only apply for a night rating when you already have a PPL(H) and 100 hours experience since licence award.
Can't help you on heli schools near London I'm afraid.
NS