As far as I can tell, there's no logic to this post in the Economist's EU blog. We are told:
To date, the best guess of British officials and politicians watching the referendum row is that Mr Brown will eventually get away without a national vote, for the reason that the Conservatives under Mr Cameron can only hammer away at the topic for so long but will then have to drop it. This is because Mr Cameron is determined to avoid the fate that dogged so many Tory leaders in recent years, of being defined by Europe. Banging on about a referendum, crudely, may chime with the specific views of British voters, if you invite them to think about the new EU treaty. But most British voters, much more importantly, do not want to think about the new EU treaty, or the EU at all. Their irritation with Europe is such that any party that talks about it, even to attack it, ends up incurring their wrath. That is what happened to the Conservatives under John Major, when any number of loons and bores on Europe became the public face of the party.
So if Labour doesn't consent to a referendum, they risk... the Conservatives screwing up their election campaign. Huh? Either campaigning for a referendum is an effective election strategy, in which case the threat of Cameron doing so would put pressure on Brown, or it's a losing proposition, in which case Brown should wish that Cameron take it.