Fresh salads are good over Christmas to counteract all that rich food and roasted vegetables. There are quite a few 'hardy' lettuce and endives or chicories you could sown around now. You could sow American Cress (Land Cress) which will give you some nice spicy watercress like leaves at that time.
Although Chinese greens aren't to everybody's taste, you could grow Pak Choi or Mizuna greens and use the leaves as salad or stir fried.
It might be pushing it a bit, but you should be able to get some baby carrots by then as well if you sow an early stump rooted variety. They'll germinate quickly now but should make enough growth in the autumn for a fresh crop at Xmas.

New potatoes for Christmas dinner! Yummie. Lol

My only thought is that if we have any early frosts planters and pots may suffer more than the open ground will. Keep them wrapped up if any frosts are forecast and you should be OK!

Thanks to all, will try wraping my pots in buble wrap!!