Well I'm lost for words (and that's unusual for me, or so my wife says !).
Thanks to all of you for sharing your experiences with me. I'm beginning to wonder if I've fallen foul of the Ray Mears marketing machine from the sound of many of you.
It's such a confusing array of kit out there it's hard to know where to start with it all. However, there do seem to be some obvious things I can do now without spending another penny for the moment.
I am heading off on Monday, so this staggering weight problem (quite literally) has been a bit of an unexpected last-minute setback, with not much time to sort it out.
I'll read through these comments quite a few times more over the w'end, and give some serious thought to whether some of the potentially optional stuff (like the axe, shaving kit, stones etc) are really necessary (I can see that they're probably not now). With respect, possibly a bit of a harsh comment about "if you can't trust your navigation you shouldn't be out"; we all have to start somewhere. If we all stayed at home until we could completely rely on our nav skills, we would never get out because we'd never allow ourselves to take that first step. If you can't be out there until you can nav perfectly then you'll never get out there, because you can't learn to nav perfectly unless you do get out there - catch 22. It's just a case of limiting what you do and having a bit of help from technology as a backup to verify my practice attempts.
As for the sleeping bag I am limited by moral beliefs on that one (I'm a vegan) so I can't use a down bag on principle (please don't make fun of that, it's just what I believe in - I'm sure no one here is like that, but you'd be surprised how much stick I have to put up with on some other forums), but the blanket idea is a good one, especially as the weather gets milder now. The Woodlore bag is heavy (about 1.5 kg I think) and the Karrimor sack is even heavier (about 2.75 kg).
Some of you may start seeing some of these items on eBay from the advice I've seen here, but once I've completed that first trip I think it will help a lot to see what was important and what was just a waste of space.
Many thanks again to everyone who offered advice. I'm positively blown away by how helpful you've all been, and if anyone else is going to Dartmoor next week to do a bit of "bushing", keep an eye out for a balding, fat g!t bent double under about 2 tonnes of bergen, then come over and say hello, it'll probably be me !!
Thanks again everyone.