There aren't many commutes of any distance in London that would be faster by car, train or bus. And depending on your ability to deal with horrible traffic, claustrophobia and general ******baggery, even a ride home at 11pm in 38 degree wind and rain can be more comfortable than the alternatives.

Like everyone has said, more than 45 min and the average person will start to think about bagging the bike for another option. That is also the point where it might actually be faster, in London anyways, to take motorized transport.