[sarajane]

I've had dahlias overwinter in the ground but only in very mild winters and in sheltered positions.

 Perhaps if you don't want to dig them up now,(its obviously mild or sheltered where you are)  I'd cut down the top growth and cover them with lots of fleece or straw if you can get any to protect them from the spring frosts we will undoubtedly get and fingers crossed they will re-sprout from the tubers they will have formed and have even bigger and better plants this year.