Hi Jaylou - and anyone else that might be interested,
If you have a look at vodaphone.co.uk, you'll see that you can buy a Vodaphone dongle for about £40 of which £15 is 'useage'. (Hubby says you get one gigabyte for that - sorry, that means nothing to me!).
If you're just using it for Minimins etc it will last for ages, though obviously not if you're downloading music or film. You can easily find out what money you've got left, and when nearly empty you can recharge it with your credit card!
It's called "Vodaphone TopUp and Go", and it works ANYWHERE a mobile phone does. You just buy it from a Vodaphone shop - there's no contract or anything.
We often stay at Travelodge, who DO have wi-fi, but charge around £5 per hour! (I'm SO slow, it would have cost me that to key this in!!!).
It also proved invaluable when our internet provider went down a few weeks ago...