Freedom pop's premium deal now is 2.25 GB of data with unlimited minutes and texts, on a month to month contract for only £6.99. The first month is free, so you can try before you buy, and Quidco are currently offering £8.80 cashback (or Topcashback £8.40 if you prefer). They also on 4G.
A couple of watch-outs - they use 3's network, and if it is like it was when I last used their free sim, you have to install their app which caused a few problems for me when I used it on my dual sim phone (basically I couldn't get the second sim to work until I uninstalled the app).
If you don't like the premium service in the first month you can drop down to the free service, which offers 200MB of data, 200 minutes and 200 texts which would do for a light user or spare phone.