David,
as you've had no answers I'll jump in. I can't swap tales because I don't have a GT40 yet and you might not be interested in my current ride.
However there are two circuits, Goodwood and Brands Hatch within 'reasonable' distance of London, maybe an hour if you've got a car. There are some events but no racing going on during your visit as below :-
GOODWOOD Check out their web site @
www.goodwood.co.uk
MON 24 OCT CLUB FIORANO - Ferrari's
TUE 25 OCT CLUB FIORANO
WED 26 OCT MITHRIL RACING - Corporate & Track Days
THU 27 OCT MITHRIL RACING
FRI 28 OCT MITHRIL RACING
SAT 29 OCT PORSCHE CLUB GB MOTORSPORT LTD - Porsche's
MON 31 OCT HONEY MONSTER RACING - Track Days
BRANDS HATCH Check out their web site @
www.motorsportvision.co.uk/brands-hatch
Don't seem to have anything on during your visit but do check.
If you have an interest in the early days of motor racing then a visit to Brooklands is always interesting as it was a race circuit and aerodrome between the two world wars. Good museum and aircraft too. You can also get there by train as its just outside London. Check out
www.brooklandsmuseum.com
Hope this helps and have a good trip.
Cheers,
Ian