Yes, many thanks for posting this amazingly comprehensive information.

Saved me some money when I was in London recently and my hotel's clueless concierge could recommend nothing other than the tube, cab+LHR Exp, or cab to get to the airport. Time and comfort were important but I didn't want to spend 45+ quid for a cab. Used this thread and within 2 minutes had called Airport Direct to book a car for only GBP23 (from WC2/Covent Garden area to LHR for 2 people) on short (1.5 hours) notice.

P.S. I would definitely use Airport Direct again in the future when the tube isn't an option.

P.P.S. GBP23 fare to LHR was only valid if paying cash. The phone operator did mention they tack on a hefty surcharge for credit card payments.