I was working in Hammersmith last summer and riding from Leyton, which was a total of 28 miles through London. It was fantastic, I got very fit and it made riding at the weekends much more pleasurable.
I’m riding to Kensington not which is a paltry 22 mile round trip and would happily ride all weekend if I could, on or off road. Even on a bad day when it’s windy, raining and generally miserable I’d rather be going to work on my bike than on public transport as I find it utterly depressing.
Do it, you can eat what you want, get fit and if clears your head. If you’ve had a bad day take it out on the road, put a few lung busting sprints in and by the time you’re home, you’ll have forgotten what the problem was.