UPDATE 1-Whoever triumphs in UK election, it won't be the press "wot won it"

* Dwindling sales makes papers less relevant

* Politicians changing tactics to mirror change (Updates with Brand endorsement of Miliband in para 5)

By Paul Sandle and Kate Holton

LONDON, May 4 Rupert Murdoch's British tabloid famously crowed "It was the Sun wot won it" in 1992, claiming its support had swayed 10 million readers to back John Major's Conservatives to an unexpected election victory.

In the three elections that followed, the rightwing paper backed the other side, helping to deliver victories for Tony Blair's newly pro-business Labour Party.

But today, with circulation figures crumbling and no party likely to secure a majority in the May 7 vote, the screaming headlines of Britain's notoriously partisan newspapers are failing to have the impact of old.

In a move that would have been unheard of a few years ago, opposition Labour leader Ed Miliband gave an interview to Russell Brand, a comedian with 9.6 million Twitter followers and his own YouTube channel.

Brand, who previously told his audience not to vote, rewarded Miliband on Monday with a surprise endorsement.

Miliband even tweaked Murdoch during the interview, saying the Australian-born magnate no longer had the power he once had: "The British people have a lot more sense than some of these papers give them credit for."

Comparing Brand to Murdoch, Charlie Beckett, media professor at the London School of Economics, said Miliband's move made sense: "Russell may get better cut through than Rupert."

David Yelland, a former editor of the Sun and deputy editor of Murdoch's New York Post, acknowledged that press barons hold less sway than they once did.

"It's quite clearly the closest election for a long time, so you would think that the print media would have a huge influence over which way it's going to go. But I don't think they do in the traditional sense," he said.

"The era, both here and in the U.S., of newspapers endorsing candidates and the feeling that that carries weight, that has gone."

Sales of newspapers, which have long been in decline, have fallen by 28 percent, or 2.8 million daily copies, since the last election in 2010 according to official ABC figures.

The industry is still recovering from a scandal in 2011 when Murdoch shut the Sun's News of the World sister paper after revelations its reporters illegally eavesdropped on voicemails of thousands of people.

A lengthy public inquiry revealed uncomfortably close ties between press bosses and those who run the country. A former News of the World editor, who had later served as Prime Minister David Cameron's spokesman, went to jail.

With most of the press leaning right, the Labour Party in particular still works hard to counter negative headlines.

"The problem is if someone reads a hostile paper day after day, after a period of time they might start believing the nonsense that's being written," prominent Labour politician Sadiq Khan told Reuters on the campaign trail.

But in an era of instant news on the internet, papers have turned to ever more inflammatory headlines, which appeal to their core readers but make them less likely to persuade others, including the wavering voters politicians need to reach most.

Pollster Populus puts voters into six broad categories and says only two of them are generally targeted by newspapers: traditionalists courted by right-leaning papers like the Daily Telegraph and Daily Mail, and urban sceptics drawn to smaller left-leaning papers like the Guardian.

"Given the blanket media coverage they tend to attract by the political press, it may come as a surprise that taken together the two groups make up less than a fifth of the total electorate," the polling group said.

Nor can even they be reliably counted on to back a particular party. Traditionalists might back the Conservatives, the anti-EU UK Independence Party (UKIP) or even Labour. Sceptics might back Labour, the Liberal Democrats or the Greens.

Politicians already know that there are more categories of voters than newspaper editorial positions.

Gavin Barwell, from Cameron's Conservative party, fighting to keep his seat of Croydon Central in South London, says he adapts his message as he goes door to door.

His team have segmented voters into about 40 different permutations so they can tailor the message to each, with a different pitch for someone tempted by UKIP than someone considering Labour.

Even Murdoch himself is now tailoring his message to fractious voters.

Last week, the Sun came out with its endorsements. Its English edition backed Cameron, giving as one of its main reasons the need to halt the influence of the "saboteurs" of the Scottish National Party (SNP). But the same paper's Scottish edition enthusiastically endorsed the SNP.

In England, the Sun superimposed the face of SNP leader Nicola Sturgeon on the body of singer Miley Cyrus swinging from a wrecking ball. In Scotland, it depicted her as Princess Leia from Star Wars and called her "a new hope".

Media commentator Roy Greenslade, a former editor of the Daily Mirror, said the decision to adopt opposite stances in two editions of the same paper was part commercial: Murdoch likes to be on the winning side, predicted to be the Conservatives in England and the SNP in Scotland. Both stances, Greenslade noted, also hurt Miliband's Labour, which Murdoch opposes.

But the moves also reveal cynicism that has cost Murdoch and fellow media barons influence.

"Deciding that politics is a plaything, you don't have to have a particular central principle. Your guiding principle is simply against something," Greenslade said. (Reporting by Paul Sandle; Editing by Peter Graff)