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[/audioplayer]‘Nothing except a battle lost can be half as melancholy as a battle won,’ wrote the Duke of Wellington after Waterloo. David Cameron may well feel the same about referendums on 24 June. The EU debate is already taking a toll on the Tory party and his premiership. While defeat would be disastrous for him, even victory will come at a heavy political cost.

Victory is, for now, still the most likely outcome. Barring a dramatic worsening of the migrant crisis or another eurozone emergency, the uncertainty inherent in leaving the EU will probably mean that most British voters will choose to maintain the status quo. But in winning the referendum, Cameron could well lose his party.

He had always believed that the number of outright leavers in the Tory fold was relatively small. At the start of the year, No. 10 thought that both Michael Gove and Boris Johnson would be onside. They thought the number of MPs backing ‘leave’ would be in double, not triple, figures. But now Cameron finds both Gove and Johnson taking on frontline roles in a ‘leave’ campaign supported by close to half of his MPs and most of the party’s activists.

The Conservative leadership has long hoped that the party could be put back together after the referendum. The idea was that the consoling prospect of a decade in power if the party stayed united would overcome the bitterness of the EU debate. But the blue-on-blue attacks are now increasingly vicious, and will not easily be forgotten. In the last few days George Osborne has slammed Leavers as ‘economically illiterate’, Boris Johnson has accused David Cameron, George Osborne and Theresa May of misleading voters about immigration, and Osborne’s warning that leaving the EU would cost households thousands of pounds has been rubbished in the most personal terms by Brexit-supporting backbenchers.

Cameron knows that he must try to stop this before the damage is irreversible. One minister in the ‘leave’ camp, summoned to see the Prime Minister recently, expected a dressing-down after criticising government policy to make a campaign point. To the minister’s surprise, the conversation was civil. I’m told that only when Boris Johnson’s name came up did Cameron show anger.

In private, those close to Cameron say that the reason more Tory MPs than expected are backing Brexit is because of either constituency pressure or personal ambition. But it is actually part of a broader trend — the British centre-right is not as keen on Europe as it once was. It is an intriguing and significant fact that all four living chairmen of the 1922 Committee of Tory backbenchers—Edward du Cann, Archie Hamilton, Michael Spicer and Graham Brady—are for ‘leave’. Given that the chairman of the ’22 is elected by his Tory colleagues, this is an good indication of where Tory parliamentary opinion lies on the European question.

The most recent ICM phone poll suggests that more Tory voters will back ‘leave’ than ‘remain’. So Cameron will need a large Labour vote for ‘remain’ to win the referendum, which explains his willingness to be photographed with Neil Kinnock last week. But relying on Labour is not a comfortable experience for a Tory Prime Minister. First of all there is the fact that Alan Johnson, leader of the ‘remain’ cause for Labour, is —in the words of one Labour insider — ‘not a driven politician’. Government insiders are already grumbling about his work rate.

This is compounded by the fact that, Jeremy Corbyn, the Labour leader, is not inclined to make life easy for the government during this referendum. He may be on the same side as Cameron in the EU debate, but he is not holding back from criticising the Tories, despite the official ‘remain’ campaign’s attempts to quell criticism of the Prime Minister on the grounds that he is their cause’s principal advocate. It’s a strange turnaround. The Tories were historically more pro-Europe. In the 1970s it was a Tory Prime Minister who took Britain into the European Economic Community and a Labour one who was obliged to offer a referendum on membership to prevent a split in his party. The left only started to fully embrace the European project after Commission president Jacques Delors’ speech to the Trades Union Congress in Bournemouth in 1988. His message was that the internal market would be a social market where ‘it would be unacceptable for unfair practices to distort the interplay of economic forces’.

At Maastricht in 1991, John Major negotiated a British opt-out from the social chapter, only for Tony Blair to take us back into it after the 1997 election. By the time David Cameron came to renegotiate our terms of membership, reviving this opt-out was no longer a realistic option: European social protections are now intertwined with the single market, so you can’t have the trade benefits without accepting substantial regulation.

Some on the centre-right who once accepted diminished sovereignty as the price of improved trade have turned against membership thanks to this extra burden of red tape. Even Jean-Claude Juncker, the current European Commission president, admitted this week that ‘one of the reasons that European citizens are stepping away from the European project is that we are interfering in too many domains of their private lives. And too many domains where the member states are better placed to take action and pass legislation.’ But there is littlechance of him doing much to fix the problem.

This volte-face by the British centre-right will have profound and lasting consequences, even if the nation votes to remain. It means that the next leader of the Tory party is more likely than not to be an ‘outer’ and that this referendum will not settle the issue in the way Cameron hoped it would. One Tory leaver points out that eight years after a Labour PM held a referendum on Europe and urged Britain to stay in, his party had a manifesto commitment to withdraw. Even if the Tories don’t follow such a dramatic course, it’s unlikely that it will take -another 40 years before we are once again asked to vote on our membership of the EU.