Defrost the turkey in a bag in a cool room. Remove the bag and giblets.

Once it's thoroughly thawed, cover and store in the fridge, and cook as soon as possible. Do not re-freeze once thawed.

To roast: This is a rough guide, because different cookers vary: Weight: 5lb (2.25kg). Thawing time: 15 hours. Cooking time: 1 and three-quarter hours to 2hrs.

Weight: 10lb (4.5kg). Thawing time: 20 hours. Cooking: 3 and a quarter to 3 and three-quarter hours.

Weight: 15lb (6.75lb). Thawing: 20 hours. Cooking: 4 and a half to 5 hrs.

Weight: 20lb (9kg). Thawing: 30 hrs. Cooking: 5 and a half to 6 and a half hrs.

Weigh the bird after stuffing the breast to calculate the cooking time, to be ready 30 minutes before carving.

Place in a roasting tin and cover with buttered foil.

Place in a pre-heated oven at 190C/375F/Gas Mark 5 for the calculated cooking time.

Baste every 45 minutes and remove the foil for the last 40 minutes to brown.