The decision about when and how to take on the tabloid press is never an easy one for governments. Get it wrong and you look thin-skinned, defensive, even paranoid. But now is just the time for Labour to challenge the Sun over its coverage of Gordon Brown in general and of the Jamie Janes story in particular.

This could be a defining moment in the relationship between Downing Street and the media. The Sun revels in its reputation for striking fear in those political leaders in chooses to demonise. It would like nothing more than to go into yet another election campaign as Britain’s most talked about and powerful newspaper. Labour will be doing everybody outside of News International a favour if it can show that those days are gone.

As the readers’ polls and email comments to every news organisation ??? including the Sun ??? show, the paper got it wrong this time. Its coverage was so vindictive and blatantly unfair that it succeeded in winning sympathy for the prime minister, not an easy thing to do these days.

Lord Mandelson was shrewd to use this opportunity to draw attention to what he called the “contract” between the paper and the Tories. With the public already questioning the Sun’s motives, now is exactly the moment to prepare the voters for more of the same and ??? crucially ??? to warn the BBC and others of the risks of following the tabloid agenda too readily.

With so many people now getting their news and analysis online or via their mobiles, the power of the newspapers to influence opinion will be at an all-time low in the coming election. It was never as great as some chose to believe. Labour’s wooing of the tabloids for the past decade and a half was born out of a misguided belief that it really was the Sun “wot won it” for John Major in 1992.

The party has no choice but to confront the Sun. Labour is not going to get its support back so it must neutralise the damage it seeks to do as effectively as possible. But it is in a stronger position to do so than any party had been in before. The paper understands that and is already rowing back. For the first time this morning it described the prime minister’s letter as “well-meaning”. Brown has shown great dignity and patience in the way he has spoken both to and about Mrs Janes.

Labour won’t want to prolong the story. Nor will it draw much comfort from the perception that the prime minister has been badly treated. You don’t win elections on the basis of voters feeling sorry for you. But if there is a lasting impression that “It was the Sun wot spun it” then the party may have helped inoculate itself against future attacks.

Labour will almost certainly go into the next election with its lowest level of newspaper support for a generation, but that doesn’t mean it has to fight with its hands tied. As Lord Mandelson said, “the public will be the judge”. And with luck they will reach their judgment having treated the evidence of tabloid journalism with the scepticism it deserves.

so don’t buy or believe The Sun