Thank you all very much for your replies!
I have been doing some research and TFT central was very useful. There are some possibilities:
Asus PA248QJ or Asus PA248Q (Not sure what the difference between the two are)
Dell UltraSharp U2412M (The cheaper option)
Dell UltraSharp U2413 (The more expensive option)
I am now leaning towards the Dell UltraSharp U2413 but what worries me is what I read on TFT Central about calibrating the monitor: “you can ONLY use the X-rite i1 Display Pro colorimeter. Other devices are NOT compatible at all”. This would cost me another £160 http://www.amazon.co.uk/i1-Display-Pro-PC-Mac/dp/B0055MBQOW/ref=sr_1_2?ie=UTF8&qid=1374425461&sr=8-2&keywords=xrite
Do I need to calibrate my monitor straight away as Dell say they calibrate the monitor for you? Or is it something I should get later on?