My front door is open everyday, from dawn till I go to bed. In my case it's because I live in rented bungalow and they won't let me put a cat flap in. So, I have to leave the door open so I don't have to keep stopping what I'm doing to let the cat in and out.
I don't live in London either. But being as most burgularies are opportunist governed, perhaps an open window would be more inviting than an open door. After all, if a front door is open wouldn't it be more likely that someone were there and have left it open for a reason. Whereas an open window, could easilly have been forgotten, if someone had popped out?