Visit O2 - Free SIM and you can get up to 4 free SIM cards. I discovered this yesterday - very useful, as I'm about to buy a second-hand iPhone...
Yes, I looked into this. It seems that if I want to use the internet frequently, I'll need to buy a £10 a month bolt-on - data traffic on standard pay as you go rates is £3 per MB which is a bit steep. You can use it with any O2 SIM card, according to the website. We shall see how I get on when the card arrives!
Great offer. Thank you for sharing the link. This is exactly what I needed. Your help is very much appreciated.