You can grow winter salads. No extra heat is required — it is sufficient just to be able to keep the weather off. I sow land cress, mizuna, corn salad, coriander (no, really), miner's lettuce / claytonia, mustards (particularly the Oriental varieties: Green-in-Snow, Red Giant and so on). They grow quite slowly, but sufficiently to keep you in welcome fresh greens through the worse of the weather, and I find that the types I've just listed combine very well on the plate to give you something really flavoursome.
You can also, for the next month, sow lettuce and mustards as micro-leaves in seed trays and flats. They will be finished by November, but they're rapid growing and a good stop-gap before the slower winter salads proper come on stream. There's a thread about them
here.
Allotment, but little achieved.