Ok, I have as usual taken my own slant on this.
And combined elements of all suggestions.
It's not cold enough to do this outside yet and I'm filling up all available fridge and freezer space with homemade produce for Christmas already. So long brinings in the fridge were out of the question
I bought a 7kg frozen turkey that is being sold half price at the moment, to ensure I got the worst possible starting material
I took a gallon of water, 225g salt, 225g dark muskova sugar. I added a whole halved onion, several carrots, a pile of potato skin peelings from sunday lunch, a good teaspoon of allspice and two prongs from a star anise, a good grate of black pepper and a big handful of home dried mushrooms. I simmered these for a goodly while then let them cool.
I put the liquor from the stock in a 5 gallon bucket in the kitchen and pitched in the still frozen turkey 24hrs before I wanted to cook it. 18 hours later I pulled the still almost frosty giblets out and got them on for gravy. Come cooking time the bird was nicely defrosted. I poured off the stock and filled the bucket to the brim with cold water, left that 5 minutes, then drained the bird. I put the wet bird on a tray in a roasting dish in a fan oven and set it to 240 deg C, when it got to temperature I gave it 10 more minutes, then turned it down to 180 deg C, covered the breast with a double layer of tin foil and the whole bird loosely with a single sheet. I cooked for about 2 hrs until the thickest part of the breast was 170 F and let it rest for half an hour.
Possibly the nicest turkey I've ever eaten...
12 year old son: I don't normally like breast meat but this is delicious.
Wife: I didn't want you to do this because I thought brining would make it salty, but this just tastes like really good turkey with a really good gravy, without the need for gravy.
Wow, I can't wait to try this with a decent turkey.