Per London Transport "Travelling in London" brochure for 2000, prices are slightly higher. I won't list them all, but for example, one day Travelcards are L3.90 for zones 1 and 2, L4.70 for all zones (1-6).

Visitor Travelcards are great if you'll be in London for more than a couple of days. If you don't have time to obtain them before you leave on your November trip, you can purchase them at the LHR location, but not anywhere else in London.