Training this winter

Yeah but...

It's still a commute. Chances are you'll burn out (slowly over time) whilst getting very few gains. Why not keep the commute strictly for easy or recovery miles?

You'd get far more benefit going out once or twice a week specifically to do repeated over-geared downhill efforts, or repeated sprint efforts; or getting out on the open road in proper training mode and doing a fartlek style ride.

Well, by now everyone knows what I think about exerting yourself during commutes (it's rubbish), so I'll move along...

he's right you know. before injury cut down my riding i did very little commuting but instead did a couple of 30-40 mile midweek lunchtime rides of varying intesity, usually a warm-up to to Richmond park a 1-3 fast laps with varying periods of 70-80-100% effort and a warm down on the way back. same weekly mileage as somebody commuting but far more effective at maintaining/improving fitness.