I'm a new Allotment grower and I've just bought some winter lettuce seeds that I hope to get in as soon as they get here. I'm wondering if I need to cover them during the winter. It's always touch and go if we get frost here in the Midlands. I don't have any Cloches but I do have some small polythene tunnels that I'm not using, I'm wondering if I should use those.

Thanks!

A tunnel on its own can make things worse. Since your coldest nights probably follow a fresh snowfall, and because snow has excellent insulating capacity, plants outside under a blanket of snow will fare better than those in a tunnel.
If you can get your hands on some spun-bonded row cover, lay that on the plants starting in November and then erect your tunnel over. If not, skip the tunnel.