Last year I bought a turkey from Asda, there was a good selection and they sell free range at a reasonable price. But if you have the nerve to shop for groceries on Christmas eve you can get some fantastic bargains.
I had to pop to Sainsbury's then to buy something and they were marking down all fresh produce to pennies just to get rid of it. So what I'm doing this year is buying a chicken now and then taking a chance on a bargain Turkey on Christmas eve.
Good luck, Merry Christmas.