The Media Column: 'For now, only one vote counts, and the Daily Mail has it'

"For you, Tommy, ze var is over." It's not a particularly welcome announcement. For British soldiers in the Second World War, the moment of surrender must have been ignominious. And reading the comments of David Yelland, editor of The Sun, last week in the Financial Times, that's rather how the Daily Mirror's editor Piers Morgan must have felt.

A few years ago, all was clear. The Sun and the Mirror were bitter red top enemies – as were the Daily Mail and the Daily Express in the middle market. The distinction was marked – rather akin to that 1960s Frost Report comedy sketch about class. John Cleese was the broadsheets, Ronnie Barker the upmarket tabs and Corbett the red tops. They had little to say to each other, and were vying for entirely different markets.

But now, it seems, all that's changed. Ronnie Corbett has bought a pair of platform heels, and today's real battle lines are between Yelland and Dacre: The Sun vs the Daily Mail, not the Daily Mirror. In that FT interview last week, The Sun's editor laid into his Mail rival with astonishing vigour: "Out in the cold, barking at the moon, and nobody's listening", was his swaggering claim. It all smacked of desperation. And Yelland almost ignored the Mirror entirely. That's not to say that The Sun really believes that many of the Mail's two million readers can be poached. They can't. Like Ronnie Barker in that sketch, Mail loyalists look down on Sun readers and very few of them can ever be persuaded to switch. No, this war is not for readers, but for influence – and here The Sun has good reason to feel much less secure.

When Labour came to office, this was the paper that claimed the credit, having ditched Old Tories for New Labour. "It Was The Sun Wot Won It" shouted the front page. And it seemed that Labour agreed. At drinks parties and receptions, it seemed the keys to Number 10 were theirs. Rupert was happy, Tony was happy: this was Yelland's heyday. Last year, despite backing Blair, the paper could hardly claim the same. They'd changed the locks at Number 10. No more invites for prawns and champers with Tony. It's as if The Sun's support had been taken for granted. And here's why: it had. After plumping for Blair over Major in 1997, The Sun was hardly going to back Hague now. Dramatically switching sides to back a winner is not a trick it can pull so easily again: once that ace has been played, it's a less useful card.

So it is for The Sun. So long as Tony Blair remains Labour leader, the party will get that paper's support at election time. Yelland has even blown the paper's gaffe for any upcoming referendum: if (as is still fairly likely, particularly after the Irish referendum result came through on Sunday) Blair calls a euro vote for next autumn, then The Sun will call for a No vote in the plebiscite – but still return to Labour at a subsequent election.

If The Sun's course over the next years is predictable, the same is not true of the Daily Mail. Of course, it's Tory-minded – but so is Blair – and it didn't think much of Ian Duncan Smith. Of course, it's generally anti-euro: but remember that it's also obsessed with home ownership. And therein, I think, lies its room for manoeuvre. Imagine, for a moment, the Daily Mail front page on the referendum's morn. On the one hand, it could go with IDS, with Sir Stanley Kalms of Dixons, with Tony Benn and Bill Cash: "Vote No for our democracy!" But look at the tempting alternative. Blair, Kennedy, Clarke, most of the CBI and the TUC. "Vote Yes for £20 off your monthly mortgage!" If the Mail can be persuaded that a Yes vote will lead inevitably to lower interest rates, then my hunch is that its recommendation will follow its readers' wallets.

All of which must infuriate Yelland. Unless there's a sea change at the helm, he is locked into support for Blair and opposition to the euro, while Dacre basks in the sunny uplands of Blairite flattery. All of us may get a vote in the referendum, but for the moment, only one vote counts, and the Daily Mail has it. My conviction is that, if (and, agreed, it's a big if) Tony thinks that the Mail will vote Yes, then there'll be a referendum next October. After all, "It's The Mail What Won It" has a nice ring to it.

c.courtauld@independent.co.uk

David Aaronovitch is away