Tesco Sim Card for £4.89 has £10 top-up included but doesn't mention the fact that you will also receive an extra £10 free call and web credit. They class the 1st £10 included as if YOU topped it up therefore giving you the extra free credit. It also has 20p to start with. Just register for everything calling 282 from the phone (free) for clubcard points and your 5 favourite numbers. Credit takes a couple of days, tops, to arrive but it does work.
Tesco Sim Card £4.89 with £20.20 credit (£10 free credit expires after 30 days)