Well I'd be glad to do it, except that my taildragger is on a private category CofA so I can't do instruction on it (unless you're interested in a share in a very nice vintage 4-seat taildragger based at Booker, in which case the syndicate I belong to gets a new member, which we could do with, and I'll do your conversion for free).
Or if you're buying an aeroplane or an aeroplane share anyway, buy it, and get a suitably qualified freelance instructor *cough* to do your conversion in what you'll be flying.
On a more commercial basis, look at
(1) Airways Flying Club at Booker (Chipmunk) or,
(2) West London Aero Club at White Waltham (Piper Cub), or
(3) Pilot Centre at Denham (Citabria).
All three are nice airfields with well looked after aeroplanes and a choice of well regarded instructors. All are within half an hour's drive of Heathrow. Nothing much to choose between them to be honest.
G