Gordon Brown today moved to lift Labour's depressed morale on the first day of its pre-election conference by mounting a populist warning to reckless banks that he will use new laws, and unprecedented ministerial pressure, to demand they rein in bonuses.

As party officials tried to portray the conference as the start of a concerted fightback, Brown insisted in an interview: "I do not roll over" – but admitted he had thought privately as to whether he was the right man to lead Labour.

In a move to pitch Labour on the side of the middle classes, and portray the Tories as once again the unreconstructed allies of the rich, Brown is attempting to capture a bash-the-bankers mood in the country at large.

But as senior ministers lined up in weekend interviews to demand that the party finally takes the fight to the Tories, Brown, on-air on the BBC's Andrew Marr Show, suffered the indignity of being forced to deny that he was on anti-depressants. The line of questioning infuriated Downing Street aides already angry that a denied rumour in the rightwing blogosphere had been pursued by the mainstream media.

Meanwhile, the chancellor, Alistair Darling, in common with the French finance minister, Christine Lagarde, will call in bankers this week to issue his toughest warning yet that he will act against bonuses and will have public backing to do so. Both claim they now have the support of G20 leaders, who met in Pittsburgh last week to demand collectively that banks focus on rebuilding their capital base, rather than paying out unjustified bonuses. Ministers want action to rein in what is expected to be a bumper round of bonuses at Christmas.

Regulators will have the power to force individual banks to build their capital base if they continue to pay excessive bonuses.

It is also likely Darling will demand greater transparency, with boardrooms required to do more to publish salaries below boardroom level. He will promise "legislation to end the reckless culture that puts short-term profits over long-term success".

He will tell the conference: "It will mean an end to automatic bank bonuses year after year. It will mean an end to immediate payouts for top management. Any bonuses will be deferred over time, so they can be clawed back if they are warranted by long term performance.

"We won't allow greed and recklessness to ever again endanger the whole global economy and the lives of millions of people."

He will also stress that the bankers do not have to wait for legislation to act responsibly this Christmas.

Although Labour is not going to back caps on individual bonuses, the rhetorical shift is important, with the party moving from a mainly managerial critique of the risk structure of bonuses to a wider criticism of their absolute level.

Labour has been given polling advice that the public still responds to the idea that the Conservatives are led by privileged public schoolboys.

In another populist move, Brown is on the brink of committing himself to giving voters the power to recall MPs found to have broken parliamentary rules on expenses or standards.

The prime minister was still debating whether to include the plan in his conference speech as part of a wider theme of increasing the accountability of politics.

Brown, who will offer himself to voters as a man who has overcome political and personal adversity all his life, is desperate to come out of the conference season with a lift in the polls. He fears that if Labour remains 15 points behind the Conservatives at Christmas he will face calls from within the cabinet to stand aside.

A ComRes poll for the Independent showed the Tories on 38% and Labour neck-and-neck with the Liberal Democrats on 23%. It also showed that Labour would do better with any one of eight other possible leaders than with Brown.

Brown told the BBC: "I've become utterly convinced as I've talked to my fellow colleagues at Pittsburgh, just how far we all have to go because they're all reporting to me that the banks are just anxious to return to the bad old days. Some of them are ready to announce big bonuses that are completely unacceptable".

Brown also moved to restore faith in his ability to bring the deficit under control by saying he will introduce a law requiring the Treasury to halve the deficit by 2014. It was not clear what sanctions could be imposed if it missed the target.

Lord Mandelson, the business secretary, was one of an array of ministers to defend Brown's leadership and judgement.

He said: "As to the prime minister, I'd rather have a man who knows his own mind, grasps the picture and sticks to his guns, rather than a shallow flibbertigibbet who has not had the guts to take on his own party, let alone find any ideas to change the country."

The Labour conference is being billed as "operation fightback" with cabinet ministers admitting they are the underdogs, but insisting that if the party can regain its will to win, the election need not be lost.

The Welsh secretary, Peter Hain, said: "We must not behave as if a Tory win is inevitable," and argued that unless the party picked itself up "we might as well wrap conference up now, go home and wait for David Cameron to give that smarmy smile of his from the steps of No 10".

Many ministers were also privately pressing Brown not to dwell on his record in handling the recession, but instead on offering an optimistic prospectus for the future.