Giffgaff is the best mobile internet provider in the UK. It's not even a contest, every other provider sucks balls compared to giffgaff. With giffgaff you get unlimited internet access for 10 pounds per month on your mobile phone, which comes in extremely handy if your estate agent 'misunderstood' your inquiry about whether there will be internet available in your new apartment when you are just moving in.
For more info check out the giffgaff.com website, and when you're ready to register, click here to give me a referral bonus which is equivalent to 15 days free internet. :)