Just a note about the 256 frame.
I took the PF30 bottom bracket version of that frame.
I live in Belgium, which I guess is on par with Nottingham for the wet weather.
And this summer is wet, it is as muddy as october right now.
The 256 frame allows some water/mud to enter the frame. I didn't spot yet the source.
But it results in a very quick contamination of the BB bearings.
I serviced the bearings once, to no avail.
I contacted the seller of my XX1, and will return the BB to them/SRAM.
May be the bearings were not properly sealed, or of poor quality.
But I'm afraid it is the whole SRAM PF30 BB that is poorly designed for wet weather.
In the meantime, I found bbinfinite.com which seems to have the perfect design for this problem.
And ordered the last one they had in stock. I'm waiting for it.
All this to say, if you choose a 256 frame (which is a great frame, by the way).
Take a BSA BB, as carbon_dude suggests.
And consider investing into a compatriot Hope bottom bracket, they say "BB that stands up to British weather":
http://www.hopetech.com/product/threaded/