Whenever you've been able to get out onto the soil to prepare it properly to receive the turf, so when its neither waterlogged nor frozen. I always avoid December and January here in London, but it is sometimes possible to lay it in February, if conditions are right, although I have no idea where you are in the UK, and whether you live in the north or the west makes a massive difference. Which is why you're asked to say where you are, it makes for a better answer to your questions.
Optimum time for turf laying is actually October, but it can be done ten months of the year, in theory. I'd aim for late February early March this year, depending where you live - we don't know what else this particular winter is planning to throw at us yet.

If you look around the area where you live you may see loads of turves being delivered. Prepare your ground and cover with a tarpaulin to stop it getting frozen or too wet to lay the turf.