The Telegraph lists what the Labour rebels who are demanding a referendum on the new EU treaty want as their price for dropping this demand.
A couple of the items could possibly be arranged by an additional British opt-out, but the majority involves preventing the rest of the countries from doing what they want. For instance, to “drop plans for further extension of majority voting and stick with the provisions agreed in talks on the Nice Treaty in 2000” is just impossible – this is one of the major reasons for the new treaty in the first instance.
There is no way Brown can give in to these demands, even if he wanted to. So it will be interesting to see if they’ll actually force him into a referendum.
The problem with a referendum is what to do if the British vote No. The other countries might offer a few additional opt-outs, but anything as radical as this list will be turned down, and I’d say it’s likely the UK would be forced to leave the EU, possibly after a second referendum.