In reply to abr1966:
If you're going to be in a tent so frequently over such a long period in the UK, I'd not bother looking at an American tent.
Nothing especially wrong with such tents but they're built for a different set of needs; warmer and, especially, drier weather. You may shave a few ounces off by having an inner tent that's made of fine mesh, but you'll notice that a stiff breeze will make it chillier inside. You may think that having a flysheet that isn't quite as enveloping isn't that important, but you'll change your mind after a week's wet weather. And small is ok if you're only inside for a night or two, but it will become restrictive well before your three months are up.
So, be prepared to shoulder a bit extra weight for the sake of space, warmth and weatherproofing. If cost were no object, I'd look at Hilleberg; though not the Akto. Fine tent though it is with many happy users, I think it's too small for the period you'll be using it. I'd look at the Staika or the Nallo. The cost is enough to make you wince a bit though.
The Terra Nova Quasar has been around for a long time; it's a good tent that will meet your needs; their Voyager tent is similarly well-regarded though as a semi-geodesic style, not quite as tough. You should also look at the Lightwave G20 trek and the Lightwave t20 trail.
So you aren't short of options (lots of potentially suitable tents I haven't mentioned) and the only way to really discover what will work for you is to go and see them for yourself. See them packed, see them put up, get inside and sit up, lie down, get in the positions you would when cooking, think about what i would be like being in there for another day of miserable wind and rain and make your mind up once you've done all that. Happy shopping!
T.