I have recently sown kale and spring cabbage. Whilst it might be a little late for swedes, give them a try. I suspect that your main problem now will be getting the seeds. Our garden centers just have left overs from this years stock but we did find spring cabbage seed in Homebase yesterday.

If you can get the seed, sow Chinese cabbage and Chinese cut and come again greens like Mizuna and Mibuna. Also sow Land Cress (American Cress) which will grow well in moist ground to give you winter salad leaves a bit like watercress.