Training this winter

Commutting can be excellent training, you just need structure with it. Most I speak to fall into the trap of going hard every day to and from work, but its neither hard enough nor easy enough so they do lots of riding thats too slow to train properly yet too fast to use as active recovery.

You could argue that a shortish central London commute is useless for either in any case, so much stop and start and no bits open enough to go hard or do intervals, you usually have to ride at a speed which is safe to flow with the traffic (it's not always gridlocked, and you are usually mixing it in bus lanes) so even going steady can be dangerous at times. Staying alive often comes before training unfortunately.
I haven't found much riding in town to be any use at all, except at night where it's clear enough for a run at things, compared to 45mins on the rollers it's awful. It must be so much worse for the 9 to 5'ers.