Hello Spana - sorry, only just spotted your reply and would appreciate any help you can give.
In answer to your questions:
I couldn't be entirely sure that Plod is a "he", he has just always been referred to as a "he";
He is 18.6cm long and weighs 1220 grammes (I measured him and weighed him to work out the Jackson ratio thing);
I got him in mid-October from my MIL who is in Australia for three months and left me to look after him (back 6 January and I'm counting the days);
Yes, he has been eating, on and off (MIL says he doesn't hibernate but nods off for a few days at a time, eating in between naps);
I have been feeding him mixed veg, a bit of salad and apple;
I've also been giving him water (even though MIL said not to) as I read it on all the tortoise websites;
He was outside when he was first here and it was warmer. He has a house and a pen outside (I wasn't having him free ranging the garden as he does at home as I was terrified of losing him);
Now it is colder he is in the conservatory which, on sunny days, gets very warm (so he wakes up and eats, like today when he scoffed down lots) and, on dull days, stays quite cool (it's unheated) and so he is very sleepy, stays in his bed (a cat bed, inside a cat box, with newspaper that he hides under) and won't eat anything I put down.
I have no idea where he originally came from - the MIL has had him for 18 years. He free ranges around their house and garden as he pleases (most of their house isn't centrally heated though, hence MIL's suggestion that he live in our conservatory). In the winter, at home with MIL, he tends to live in the kitchen. He's never seen a heat lamp in his life.
Lastly, please don't shout at me
The MIL dumped him on me with the briefest of instructions and it is because I am worried that I might be doing the wrong thing and harming him that I have been trying to get some advice.
Any help you can give me would be appreciated.