THE war drums are pounding among those dreaming of a referendum on EU membership.

As noted in a post last week, Peter Mandelson, the former Labour cabinet minister, co-inventor of Blairism and ex-European Union trade commissioner, stirred things up with a lecture at Oxford University, suggesting that pro-Europeans (of whom he is one) should support such a vote, if and when euro-zone integration deepens to such an extent that Britain finds itself an associate member of a two-tier club.

Lord Mandelson's democratic analysis was hard to dispute. He noted that 56% of respondents want a referendum on British membership. He also noted that the mandate secured by the government of Edward Heath in the only ever British referendum on Europe, in 1975, "belongs to another time and another generation".

A few days after Lord Mandelson's speech, the Spectator magazine's political editor, James Forsyth, quoted a source “intimately involved in Tory electoral strategy” who stated that it was “basically a certainty” that the next Conservative general election manifesto would contain a promise to hold an EU referendum. The goal of such a wheeze, as analysed by Mr Forsyth, is twofold. First, to shut down the threat from UKIP, the anti-European party which is currently siphoning votes from disgruntled right-wing Tories. Second, to “shoot the fox” of Boris Johnson, the Conservative mayor of London who is on record as supporting a referendum on Europe.

Something clearly being up, I made some calls yesterday to well-placed Conservative and Labour sources. I put it to one Tory source that the briefing smacked of Number 11 Downing Street to me, and George Osborne. This merely triggered a lot of mumbling and coughing, alas. But I note that this morning Paul Goodman of ConservativeHome is firmly fingering the Chancellor of the Exchequer, on the basis that (a) Mr Osborne has a fondness for such bold gambles, and (b) Mr Osborne might one day find himself in competition with Mr Johnson to succeed David Cameron as Tory leader, so has an interest in shooting foxes belonging to the mayor.

Now, I suspect that I start from a different place to Mr Goodman and Mr Forsyth on this question, for the simple reason that—while I enjoy a debate about internal Tory politics as much as the next hack—I don't actually want Britain to leave the EU, so find all this blithe talk about who would gain from a referendum a little alarming.

But Mr Forsyth is on the money, as far as I can tell, with his reporting that inside Tory high command there is a sense that Mr Cameron may not have very much choice about calling a referendum if UKIP's surge carries on, and if—as senior Tories suspect—Labour makes its own referendum pledge in its general election manifesto.

As the Spectator reported, one favoured option would be to propose a renegotiation of Britain's terms of membership after the election, to be followed within 18 months by a referendum on the results of those negotiations.

I cannot improve on Mr Goodman's pithy analysis of the risks for Mr Cameron if he were to promise British voters a new deal with Europe, to be endorsed by them at a referendum at the end of negotiations with the other EU nations. As Mr Goodman points out, the rest of the EU, led by Germany and France, might tell Mr Cameron to get lost, at which point he would face the unpalatable choice of campaigning to stay in the union anyway (a vote he might lose, and which would split the Tory Party), or campaigning to leave (a vote he might lose, and which would split the Tory party). Mr Goodman offers a third scenario, which I admit I think less likely, in which France and Germany take a pause from trying to save the euro, at immense pain to their public finances, and agree to give Britain what it wants, ie, low-cost, low-regulation free-rider membership of the single market. In that case, Mr Goodman asks, what happens if Mr Cameron puts his concessions to the country and gets a No vote anyway, because the public wants to kick the government?

So, is there going to be a referendum? I don't think it has been decided, but it cannot be ruled out.

There are lots of rational reasons for Mr Cameron to fear any sort of referendum pledge. Most simply—though Bagehot accepts that this is an argument that makes many people at Westminster yawn in boredom—such a referendum might lead to Britain's departure.

And although he finds the EU exasperating in lots of ways, the prime minister does not actually want to leave the EU. He does not love the European project, instead regarding membership as something to be nudged by a cool cost-benefit analysis. And weighing those costs and benefits today, Mr Cameron thinks that the right of his party are simply miscalculating where the balance lies. For him, the benefits still trump the costs, a close ally insists.

William Hague, the foreign secretary, ends up in the same place when he conducts his cost-benefit analysis, other sources tell me, even if—emotionally—there are aspects of European membership that he finds harder to swallow than the prime minister.

Yet the Tory leadership could end up being forced into promising a referendum, agrees a senior source, either because of a surge by UKIP in the run up to the next general election, or because the Labour Party promised an EU referendum of their own.

Might Labour promise an EU referendum in its next manifesto, knowing that such a pledge would act as a wedge to split the Conservative Party? If Ed Balls, the shadow chancellor and long-time sceptic about the European single currency, were the party leader, he would probably be “tempted”, a senior Labour MP says.

In contrast, Ed Miliband genuinely is instinctively pro-European. He thinks of himself as a European social democrat, and is surrounded by close aides, such as Stewart Wood, who think the same way. His own family background (his family came to Britain as refugees from the Holocaust) inclines him to run a mile from nativist and nationalist arguments.

Moreover, Mr Miliband fears that a referendum promise would create substantial economic uncertainty for Britain in such fields as foreign inward investment, I am told. Labour also “burned its fingers in the past” by promising a referendum on the abortive EU Constitutional Treaty, only to renege on that promise when the Constitution was voted down in France and the Netherlands and was turned into the Lisbon Treaty. It would perilous for Labour to make the same mistake again, says the MP.

It is true, I am also told, that some in the party wanted the leadership to be more opportunistic in October 2011, and to ally themselves with Tory Eurosceptics in the division lobbies in the vote that saw 81 Tory MPs rebel over whether to hold a referendum on EU membership.

Yet there is a good case that such opportunism would have been counter-productive. Had Tory rebels known that Labour MPs were going to be whipped to vote against the government then many of the 81 would have abstained or simply absented themselves from Parliament. By standing back from an internal Tory squabble and abstaining, “we probably maximised the Tory rebellion,” says a Labour source. 

Yet as with Mr Cameron, the decision could be taken out of Mr Miliband's hands by a UKIP surge. If UKIP wins the 2014 European elections, “all parties would come under really intense pressure to hold an EU referendum,” says the same Labour source. “It would be pretty hard to resist at that stage.” As to whether an in-out referendum would be winnable, few British politicians are willing to bet on that any more, given the breakneck pace of events in the euro zone. “We've a better chance of winning a referendum if Labour is in power,” is all a Labour MP will say.

A final thought. If this debate strikes non-British readers as amazingly navel-gazing, given what else is going on in the euro, I understand that. But—unfortunately for Euro-rationalists like me—the chaos in the euro zone feeds directly into the British debate, turbo-charging the rage of those who want out of a European project they see as statist, sclerotic, spendthrift and doomed.

The debate of a British referendum on the EU is also being watched closely in at least some other capitals, I can report. Jose Manuel Barroso, the European Commission president, is particularly concerned.

Though a bit of a trimmer and waverer, Mr Barroso, a former Portuguese prime minister, is a free-market liberal and free trader, and an Anglophile. In his view, a British departure would be a disaster for the European project, condemning it to become much more statist and protectionist. A figure close to Mr Barroso, passing through London a few days ago, was certainly keen to know whether a referendum might be promised here.

Standing on the pavement in St James's after the meeting, the visitor from Brussels asked me, out of the blue, what the odds were of Britain leaving the EU by 2020. My instinctive response: 40%. A day or two later, I think that might be a bit low.