I live in Zone 5 and I actually think a car for me would be a more of a hassle then it is worth. The parking near the flat is permit free and I am not far from a mainline station, so the streets are filled with commuters who use the streets are a station car park. I am about 1.5 miles from the nearest tube and find that between buses and a good brisk walk, I have no problem getting around and have no worry about finding a parking spot!
