By Torin Douglas BBC media correspondent

It was the news Tony Blair really didn't want to hear.

The promise by Rupert Murdoch, Labour's media bete noire, that he'd campaign against the euro if there's a referendum on joining the single currency - and the prospect that he'd throw the full weight of his newspaper empire into the fray.

Interviewed by the Financial Times, he said his clear message would be "vote no" and he wouldn't be happy if his newspapers took a different line.

Having neutralised the Murdoch newspapers before the 1997 election - and preserved that position at the last election (despite a Sun headline asking if Blair was the most dangerous man in Europe) - the government is widely believed to have fought a constant battle to keep Britain's most powerful newspaper owner on its side.

The central issue is one of sovereignty

Rupert Murdoch

Yet, despite the relaxation of the media ownership rules announced in the government's draft communications bill - changes which could let Murdoch buy his first terrestrial TV channel - the media baron clearly has not softened his antipathy to the single European currency.

"The central issue is one of sovereignty" he said.

"If you give up control of your currency, you are going to give up control of your tax, just as night follows day."

So much for industry speculation that a deal had been done, and that Murdoch would be allowing his papers to take a softer line on the euro in return for the new rules on media ownership.

Murdoch's papers are important, not just in terms of circulation but also their influence.

Wake-up call

The Times, the Sunday Times, the Sun and the News of the World reach a huge cross-section of the British public and none is afraid to use its pages to campaign for causes it believes in.

The Sun wears its anti-euro beliefs on its sleeve.

"Wake up Mr Blair and smell le caf�" wrote political editor Trevor Kavanagh after the defeat of premier Lionel Jospin by the far-right candidate Jean-Marie Le Pen.

"While we are outside the single currency, we can continue to respond to the economic issue at the heart of the European crisis - unemployment.

"Our jobless levels are the lowest in Europe - the envy of France and Germany. The moment we sign up to the euro, we sign that freedom away."

So no change there then. But most intriguing will be what the new editor of the Times makes of this highly public expression of Murdoch's views.

Hard line

Interviewed recently, Robert Thomson cleverly sidestepped questions about the interventionist tendencies of his proprietor and his paper's position on the euro: "I know it sounds wimpy, but I think it right to wait and see."

However, he also pointed to a leading article which argued that economic conditions were not favourable and to make "a wild dash for entry... would truly be betrayal".

As the Guardian interviewer Roy Greenslade observed, that certainly didn't suggest any softening of the line on the euro.

Thomson's view of Murdoch was equally sanguine.

"The remarkable thing about Rupert Murdoch is how much faith he has in incoming editors and how much he's going to leave to you, because of his confidence in your instinct."

If his editors had any doubts about which way their instincts should be leaning, they must now be resolved.

And perhaps Tony Blair and Alastair Campbell should now devote their attention to other newspapers, who may be more persuadable.