We'll be using a car service for the first time on our March trip as it is cheaper than LHRX and a taxi to our hotel. How much time should I allow to get back to LHR from Imperial Wharf( Chelsea Harbour) . Our plane leaves around 11 Am and I want to be there at least 2 hours before flight time, so that might put us into rush hour.

ttt

Assuming your plane flight home is an international one, you need to be at Heathrow 3 hours early. Arriving at 8:00 AM, you should miss most of the rush hour. (Commute times around London are later than in the U.S.) I'd ask the car service how much time to allow for the drive. Or the hotel.

I think you are right Mimar. 3 hours would be better..and the DH needs to replenish the single malt! Good idea about asking the car service. Why didn't I think of that???

Very often the car service asks what time the flight is, and then they tell you what time they should pick you up.

I agree with the advice to arrive 3 hours early, especially since there are new regs thanks to the panty bomber. The last time I flew from LHR I arrived just over 2 hours early and I wished I had arrived sooner. I made my flight but not with a lot of time to spare.