London has one of the best public transport systems in the world. Forget ideology or saving the world, using public transport is just so much easier and more convenient than driving in London. And despite whinging about the price if you tap in/out with your bank card or an oyster card it is a lot cheaper than driving, and that is before thinking about parking costs. As I say, I prefer to walk but use public transport when it is bickering down and the system works very well.
For my journey into London I use the train, a fast train from MK central to Euston only takes 32 minutes and there is something over 100 trains a day in each direction. Even the all stops slow train is an hour, which is still faster than I could drive to Euston.