Harriet Harman did her best to inject a note of sunshine as she wrapped up proceedings at the Labour conference today after a difficult week which saw the party slide to third place in the polls and lose its most powerful media backer.

Gordon Brown's party deputy has taken over the end-of-conference slot occupied during the Blair years by the then-Deputy Prime Minister John Prescott.

But although she was never going to match Mr Prescott for mangled grammar and sheer morale-boosting ebullience, she managed to fire off a few potshots at David Cameron's Conservatives – who hold their own annual conference in Manchester next week.

Ms Harman, who serves in the Cabinet as Minister for Women and Equalities, launched a vitriolic attack yesterday at The Sun, Britain's best-selling daily newspaper, after its decision to switch its support from Labour to the Tories.

Today the Peckham and Camberwell MP appeared to be backing away from an out-and-out fight with the redtop, telling delegates: "We have made progress on equality, even in The Sun.

"On page three today there’s a young woman who’s really concerned about jobs for women as well as men. And what a coincidence - she’s called Harriet, aged 20, from Peckham.

"The only problem is that Harriet is so concerned about jobs that she’s forgotten to put her clothes on."

The Sun's desertion, announced on its front page yesterday morning, came as a body blow to the party after Mr Brown's speech the previous afternoon in which he had tried to relaunch the party around a more populist policy agenda targeting anti-social behaviour and single mothers.

Paradoxically, however, it has allowed party leaders to claim underdog status as they mount what they are calling "Operation Fightback".

Ms Harman said that this week had seen Labour's "most important conference for more than a decade" and its highlight had been "Gordon's brilliant speech".

"We have come together at this conference and we have re-ignited the fire of our passion and commitment," she declared. "You have shown – at this conference – that Labour's team is fighting back."

Ms Harman said that Labour would "continue to expose the shambles" of the Liberal Democrats under Nick Clegg, who, she said, described himself as "the man for change - but I don't think the British people will trust him even with their loose change".

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