Alan Watkins: Mr Cameron should expect a summons to the media mogul across the Atlantic

Murdoch's papers have almost alone changed the policy on Europe

Mr Tony Blair is calling on Mr George Bush before receiving rather more important instructions from Mr Rupert Murdoch; much as a visitor might stop briefly in Paris before moving on for a longer stay in Nice. The local climate is still favourable, though not perhaps as sunny as it was nine years ago. The great proprietor may withdraw his favours at any time.

Mr David Cameron and the young men and women who surround him repose the highest hopes in Mr Murdoch; or, at any rate, they did, before he made a few disobliging observations about the new Conservative leader, to the effect that he was all show and no substance. Mr Murdoch remains Mr Gordon Brown's supporter, for the time being, at any rate.

My information comes more or less from these newspapers. In particular, it comes from Mr Irwin Stelzer, who writes numerous articles for the press. It is not wholly clear whether he is, so to speak, one of the Apostles, or a minor Prophet of more than usual unreliability. He is an economist by trade, and has more in common with Mr Bush than he has with, say, Mr Ed Balls or, for that matter with Mr Brown himself. Mr Brown and Mr Stelzer remain great pals.

But Mr Brown and Mr Murdoch? Ah, that is a slightly different matter. Mr Murdoch approves of the Chancellor's sturdy Presbyterian values, even though the great proprietor has been married three times and has deserted his native land to become a citizen of the United States. No matter. Mr Murdoch's concern is whether Mr Brown will duly be elected Prime Minister.

At the moment the polls do not look any too good for Labour. Additional evidence goes to show that Mr Brown will perform even more disappointingly than Mr Blair when - and if - he is replaced by Mr Brown. Of course, the women columnists of The Guardian will be enthused. We all know that. So also will numerous earnest party supporters or those of them that remain.

But will the readers of The Sun be similarly uplifted? It is very doubtful, to say the least. Mr Murdoch may be stuck with Mr Brown in default of any more attractive replacement. As we know, he is none too keen on Mr Cameron. But he hates being on the losing side in his usually well justified expectations of favours to come.

As a matter of language, I see that Mr Murdoch is routinely described daily in the City or Media pages as a "media mogul''. No doubt that is what he is, allowing for the impoverished language. In the early 1960s, before Mr Murdoch arrived in Fleet Street, I referred to a predecessor of his as a "mogul''. "Avoid that word,'' the then literary editor of the Sunday Express advised me. "It's a Daily Mirror sort of word.''

I have obeyed his injunction ever since, with no discernible effect.

In this earlier age, the leading popular papers were the Daily Express and the Daily Mirror. The Daily Mail was then in decline; while The Sun, successor to the old Daily Herald, was at this stage merely a glint in Mr Murdoch's eye. The landscape has been changed. The valleys have been exalted, and the rough places made even rougher.

In the old days, Labour's only reliable supporter was the Mirror. In the Age of Wilson, 1963-76, the greatest trouble was gone to by the Labour Party to keep the paper's editors and correspondents in a happy and contented state of mind. Titles and small exclusive stories were dished out on the one side as generously as expensive lunches were supplied on the other. The late Hugh Cudlipp, editorial director of the whole set-up, would attend the party conference with a cigar in one hand, followed by an obedient retinue of newspaper Mafiosi.

How different it is today! But all is not lost; far from it. On reflection, I would estimate, the balance has shifted: shifted not merely towards Labour but, between 1992 and the early 2000s (it is too soon after the most recent shift to be precise), against the Conservatives.

In the early days of Mr Blair's first administration, both Sir David English, the originator of the modern Daily Mail, and the third Lord Rothermere, the owner of Associated Newspapers, sadly died relatively young within a few weeks of each other. You never saw such a fuss in all your life: not, naturally, from the newspapers and their staffs, or, more naturally still, from their bereaved families, but from No 10. With assorted funerals and memorial services for the Prime Minister to attend, Mr Blair's black tie was kept permanently on hand.

Alas, it could not last. Nor did it. Mr Paul Dacre, Sir David's successor, was left indulgently inclined; as, presumably, is the fourth Viscount likewise. But for a time, Mr Alastair Campbell was able to boast that he had got both the Mail and the Sun on his side, which Labour had never managed before, for what that was worth. To Mr Campbell and Mr Blair, however, not to mention Mr Brown, that was jewellery beyond price.

The Mail proved unsteady on parade. And yet not only The Sun but the whole array of Mr Murdoch's papers has proved more reliable. If I had to mark a turning-point it was the public reception to Lord Hutton's report. Both No 10 and the Murdoch press badly overplayed their hand. The honest readers were perfectly prepared to cheer on Our Boys, in Iraq and elsewhere. What they were not prepared to do was to perpetuate a cover-up.

However, Dr John Reid is quite ready to act as Fleet Street's Home Secretary. He is merely carrying the truncheon handed on to him by Mr David Blunkett, Mr Charles Clarke having dropped it in the intervening period. The paradox is that, with popular newspaper circulation declining, the press is as powerful as it was say, in the years immediately before the First World War.

There was then a multiplicity of titles, appealing to an educated readership and circulating largely in clubland and the West End. It is not the same today. But the political impact of the Mail and The Sun is the same. The similarity is that the people who are being influenced are the politicians rather than the readers themselves.

So it is foolish to depreciate the influence of the press. Mr Murdoch and his papers have virtually alone changed United Kingdom policy on Europe, over the euro and the European constitution alike. Certainly events in the Middle East have helped to detach Mr Blair more comprehensively from Europe, as this week's little jaunt demonstrates. But as far as one can see, Mr Cameron is even more detached from the Continent. It can only be a matter of time before Mr Cameron is the grateful recipient of Mr Murdoch's hospitality in the United States.