It's simple really. I used to get to work every morning having experienced this:
...these days I gently peddle through this:
And for those who worry that cycling makes you sweaty, well of course it all depends on how hard you peddle, and in the height of summer the temperature on the platforms of the Central Line in Zone 1 peaked at 50oC this year. For me, when added into the equation of all the other reasons why I love cycling in London, there was really no contest.