The T-Mobile deal is actually better than £1 a month because they don't take your £10, you still have that left so it is actually free Internet for 12 months. After 12 months you can throw the SIM away and buy another, or as I did, top up to £20 and 'buy' 6 months more Internet.
You get 500MB data per month for streaming (youtube etc) and unlimited browsing/email.
Alternatively, if you don't want the hassle of potentially having to contact T-Mobile support (and they don't make it easy) you can buy a pre-activated card for just under £20 (and you will still have £10 credit on this).
You are advised to put the SIM in a phone every six months and make a call/text to keep it active. Worked for me. They currently are only available for the iPhone 4/4S so you will need to get yourself a SIM cutter (or decent knife) and chop down.