Did Murdoch call the shots?

The more paranoid parts of the press are saying that Tony Blair's spectacular U-turn over a referendum on the EU constitution is all the sinister work of the notoriously Eurosceptic Rupert Murdoch.

That is a gross exaggeration. But there is no doubt that the need to keep Murdoch's papers onside in the run-up to the General Election played its part in 10 Downing Street's deliberations.

"We were pushing at an open door," says my man in the Wapping executive suite. "Plenty of people in Downing Street were telling the PM that his opposition to a referendum was unsustainable. We simply helped concentrate his mind."

I understand that Murdoch and his lieutenants made it clear to Blair that if he persisted in refusing a referendum then the News International papers in general and The Sun in particular would make it the major issue between now and the election. "This issue matters a lot more to our readers than the Government realises," said one Sun editor.

This troubled Blair. It is not the loss of The Sun's endorsement the day before the election that he worries about most: it is the drip, drip of negative publicity, day after day, in the Murdoch press that he wants to avoid because he fears it would undermine his re-election chances in the much the same way that it helped make Neil Kinnock unelectable in 1992.

Murdoch and his men pointed out that it would be hard for his papers to campaign stridently over the next year for a referendum and still endorse Blair's reelection come polling day. "It would have undermined our papers' credibility in readers' eyes," said one Murdoch man.

"Blair could see the support of The Sun, which he values very much, slipping away because of his refusal to agree to a referendum." Pressure from Murdoch only contributed to Blair's U-turn; it was not the clincher.

More credit should go to Cabinet heavyweights like Jack Straw and John Prescott - but above all Gordon Brown, who wants to fight the next election on the economy and not have his achievements overshadowed by a campaign for a referendum in the Eurosceptic press.

Brown has his own hotline to Wapping. Murdoch's men knew they and the Chancellor were singing from the same song sheet. Blair became isolated, inside and outside the Government. Already pretty lonely for his stance on Iraq, he could not afford to be out on a limb over an EU referendum too.

Inside 10 Downing Street the hope is that, now a referendum has been reluctantly agreed, the EU constitution issue has been " ringfenced", just like the euro has been by the promise of a referendum, Murdoch's papers in general and especially his Sun can continue its support for Blair. But it's not that simple.