P.s. Dt770 Pro 80 ohm user!
Someone's been lurking in the headphone thread...
You list a lot of things that will make it tough to find the right keyboard for you.
You want brown, yet you state you want a Blackwidow, so may I assume you're okay with any tactile key? If so, grab a Deck with clears. I've rarely heard a bad thing about Deck, seems you're in good hands if you get one.
If that's too expensive, and you want the backlighting and 6kro, go with Xarmor. The U9BL-S was just released on Amazon with cherry browns.
Your other option is the Black Widow, but I think for the prices they charge for a Black Widow over there you might be better off going with a Deck (Black Widows are ~$150USD in Europe, right?).
Finding anything with UK layout will be hard. I don't know off the top of my head any retailers that make mech kbs with UK layout and Cherry Brows + backlighting. But I still say grab the Deck, seeing as no matter which of the keyboards you buy you'll have to pay a premium you might as well throw a few extra dollars/pounds on there to make sure it's top-notch.