Have a read of these tips from some turkey roasting veterans.
Easiest Roast Turkey
We get our turkeys from Nick & Jacob at Fosse Meadows. As well as raising the best poultry in the land, they are dab hands in the kitchen and have a range of recipes on their site for making the most of their tasty birds.
To roast a turkey, they recommend the following method:
Preheat oven to 230C/Gas Mark 8. Remove turkey giblets and reserve. Place the turkey in a large roasting pan, brush the turkey generously with rapeseed oil and season with sea salt and black pepper and cover with foil. Place the turkey in the pre-heated oven and cook at this temperature for the first 30 minutes. Then, lower the oven temperature to 180°C/Gas Mark 4 and cook for approximately 30 minutes per kilo, basting every hour. Remove the foil for the last half hour, then rest for half an hour after cooking.
See the full method on their site, here