I needed a 1GB Sim card for my Mini Ipad and have found what I thought was a good deal:
EE - 1GB = £10.00 rolling contract
Then I found this: EE buy SIM and top up £15 and get 10GB free to be used over 90 days. This deal works out better (more data!) and cheaper.
Not sure if this continues every time you top up £15.00?