I'm in the same boat. I'd advise you to wait a little longer for 4K monitors with DisplayPort 1.3 or atleast HDMI 2.0 on them.
Currently the only way to drive a 4K monitor right now is to use DP 1.2, but with that it uses MST (Multi-Stream Transport), and that uses two separate signals as it's designed for using multiple monitors over a single DP 1.2 cable (because if it don't use MST it wont have enough bandwidth for 4K @ 60hz). So Windows has to load drivers so that it treats MST as a single monitor. The problem is that on some graphics cards you wont be able to see the motherboards POST or BIOS screens, because the driver wont load until Windows starts.
DP 1.3 and HDMI 2.0 will fix this. Monitors with these inputs will start appearing late this year.
At the moment you can get the Dell UP3214Q 31.5" monitor for £1400 on here. It has DP 1.2 though. Like i say it's best to wait.
Asus are releasing the 32" PA328Q some time around November. It will have HDMI 2.0 and it should be under £1500. It will have a
AHVA panel, which is better than any other VA panels and matches IPS.
And the Seiki 32U4SEP-G02 32" monitor will be out early next year. If you care about colour reproduction and accuracy/quality then it has some beastly specs, but i've no idea how much it will cost yet. It will also have
both DP 1.3 and HDMI 2.0. There will also be a 40" version.