It's not just higher temperatures that veg need, it's higher light levels - if you provide enough of both to keep veg growing through the winter you'll have higher electricity bills!!! Much higher!!!
I sow Aquadulce Claudia broad beans in the veg patch in late October - they stood through all the snow of last winter and spring, and gave us a fantastic crop
You could sow some Arctic King lettuce in a cold greenhouse overwinter - I grew some under a large cloche last winter and they were great.
As has been said, a sowing of Swiss Chard now might give you winter pickings, depending on the weather we get, and anyway should stand through the winter to get away early in the spring for an early crop.