The Times ran an interesting article this week about new data tariffs introduced by mobile operators. While mostly highlighting prices for contracts, they also mention at the end of the article that Orange and T-Mobile U.K. are also offering web access via their prepaid pay as you go SIMs.
That's great news for three reasons: First, prices are now low enough and the terms and conditions are now easy enough to understand for allowing people to experiment with mobile Internet access. Second, especially young people are often on pay-as-you-go SIMs and were so far not permitted access at all or only at ridiculously high cost. And third, mobile access to the Internet via prepaid cards now also offers international travelers the opportunity to connect whenever and wherever they are in the U.K.
Pay-As-You-Go Web'n'Walk: 0.73 pence per kB capped at 1 pound a day. The fine print here says that the transfer volume should not regularly exceed an average of 40 MB per day. That should be good enough for most purposes. They do not mention port blocking or other restrictions such as a restriction on IM and VoIP.
According to the Times article the prepaid offer is called "Internet snacks". The price is 40p for 15 mins with daily cap of £2 or a daily £1 bundle. I tried to find the details on the Orange U.K. page but they have hidden the offer very well. I searched for 10 minutes but could not find anything so I have no idea what the restrictions of the offer are.