Tony,
Are you thinking of MacKenzie's Teignmouth? Not a bad course but not one to go out of the way for I would say, though good views on a clear day.
Jonathan,
There are more than enough heathland options around western London and Heathrow, also plenty of discussions in the past (and at present) of which ones to play on here.
Sean's route takes you down the M3, but I'd suggest heading down the M4 to the M5 as when you get to Devon the roads will be slow enough. You could also stop of at Burnham & Berrow (if Sean can't meet up with you then perhaps I could, again if we can get diaries to work), or a brief detour up the M5 could bring you the quirk of Painswick?
All others suggested are worth checking out if on a longer tour of the Devon / Cornwall area but with just a couple of days I'd suggest Saunton (East) and St Enodoc as your bets.
Cheers,
James