are there any decent mobile broadband providers ? or do they not exist?

You can't get much better than o2 broadband at the moment.

Avoid TalkTalk at all cost no matter what they offer you. They're shocking.

TMobile is the best if you can get one of the old-er Pay and Go sims, no monthly contract, and it costs no more than £1 per day, use it 1 day, pay £1, don't use it the next, don't pay.