Rupert Murdoch has never been a man to let details get in the way of a good headline. This week he accepted the accolade of being the most influential Australian of all time, even though by his own admission there were others on the shortlist who'd done a lot more to make the world a better place.

Surely he should be stripped of his title without further ceremony - and not because of the inconvenient little fact that he's been an American citizen for the past 21 years. His editors insist that he never influences the way they produce their papers. The politicians maintain that, for their part, they act in the best interests of the country, not those of Rupert Murdoch.

He may carry some clout in the boardroom, but in the cabinet room? Mr Murdoch should throw up his hands, give back the award and admit that he has no more influence over government policy than you or me. Less, in fact. At least we have a vote in this country.

In my spin-doctoring days I might have tried an argument like that, although not without that tell-tale flicker of a smile. It's true that Rupert Murdoch doesn't leave a paper trail that could ever prove his influence over policy, but the trail of politicians beating their way to him and his papers tells a different story.

There is no small irony in the fact that Tony Blair flew halfway round the world to address Mr Murdoch and his News International executives in the first year of his leadership of the Labour party and that he's doing so again next month in what may prove to be his last.

I have never met Mr Murdoch, but at times when I worked at Downing Street he seemed like the 24th member of the cabinet. His voice was rarely heard (but, then, the same could have been said of many of the other 23) but his presence was always felt.

No big decision could ever be made inside No 10 without taking account of the likely reaction of three men - Gordon Brown, John Prescott and Rupert Murdoch. On all the really big decisions, anybody else could safely be ignored.

I was reminded just how touchy Downing Street is about Mr Murdoch when I submitted the manuscript of my book, The Spin Doctor's Diary, to the Cabinet Office. The government requested some changes, as is its right. When the first batch came through, it was no surprise that Tony Blair's staff were deeply unhappy. The real surprise was that no fewer than a third of their objections related to one man - not Tony Blair or even Gordon Brown, as I might have expected, but Rupert Murdoch.

In my first few weeks as Alastair Campbell's deputy, I was told by somebody who would know that we had assured Mr Murdoch we wouldn't change policy on Europe without talking to him first. The Cabinet Office insisted that I couldn't say in my book that such a promise had been made because I did not know it for a fact. With some reluctance I turned the sentence around so that it read: "Apparently News International are under the impression we won't make any changes without asking them." Every other request relating to Murdoch was rejected. It seemed to me that the government was simply trying to avoid political embarrassment on a subject of wholly legitimate public interest.

All discussions - and let us hope the word "negotiations" isn't more appropriate - with Rupert Murdoch and with Irwin Stelzer, his representative on earth, were handled at the very highest level. For the rest of us, the continued support of the News International titles was supposed to be self-evident proof of the value of this special relationship. The Sun and the Times, in particular, received innumerable "scoops" and favours. In return, New Labour got very sympathetic coverage from newspapers that are bought and read by classic swing voters - on the face of it, too good a deal to pass up.

In fact, New Labour gave away too much and received too little that it couldn't have expected to get anyway.

Rupert Murdoch loves power and loves the feeling that he has the ear of other powerful men. Who else was going to give him that feeling? Would he get it from William Hague? Iain Duncan Smith? Michael Howard?

It may be that Rupert Murdoch has never once vetoed a government decision, nor tried to do so. I just don't know. What I do know is that, as the entries in my book show, I spent far too much time trying to stop ministers saying anything positive about the euro. When two prominent Conservatives, furious at Tory policy on gay rights and Section 28, decided to defect to Labour, I made them say that it was over our management of the economy. I attended many crisis meetings at the Home Office - the influence of the Murdoch press on immigration and asylum policy would make a fascinating PhD thesis.

Now Mr Murdoch tells us he might support David Cameron, and his papers take regular potshots at Gordon Brown. Do Messrs Cameron and Brown take notice? You bet they do. In a close election the support of News International will be courted as never before. They know that Rupert Murdoch likes to back a winner and that it is support in the country that separates the winners from the losers, but they won't dare risk leaving it to the voters. So in the meantime, Rupert, much as it pains me to say so, you can keep the award.

· Lance Price, a media adviser to Tony Blair from 1998 to 2001, is the author of The Spin Doctor's Diary lanceprice.co.uk

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