In reply to dunnyg:
Wasn't going to respond as my suggestions aren't freestanding, but there seems to be some other recommendations that aren't either so I would say it's worth looking at the Exped, Macpac and Vaude models too.
The Exped Orion is fairly sturdy, but can also exhibit problems under snow loading. Their expedition model, the Polaris, looked very good at a showcase but I haven't tried it out in the real world - and even so, it might be overkill for your needs.
Several of the Macpac range might also suit your needs, but for wind or snow shedding the Plateau is hard to beat. Some owners have reported problems, but even in less than perfect pitches I've never had any problem with it - including above the snow line in Scottish winter.
The Vaude range also has some sturdy options, with the Odyssee & Atreus (the 2 or 3 person models), being both quick to set up and reliable in bad weather.
Some of the colours look a bit bold from outside, but make for a pleasant glow inside in the morning - much like the later Quasars.
Of course if it's always going to be cold rather than wet (unlikely given the UK use...), then single skin options are superb as free standing shelters. I've used the older Rab models, but the new Latok range looks every bit as capable too.
I hope you find an option that fits mate.