David Cameron yesterday vowed to turn the Crewe and Nantwich by-election into a referendum on Gordon Brown's abolition of the 10p tax rate, piling pressure on the Prime Minister while he still faces the threat of a rebellion on the issue from Labour back benchers.

Mr Brown's struggle to get his party back on course after a disastrous showing in the English and Welsh local elections continued yesterday with former Home Secretary Charles Clarke challenging him to change his leadership style and abandon controversial plans for 42-day detention without charge.

Mr Cameron, who headed off yesterday on the campaign trail to Crewe, said the abolition of the 10p tax would be the key campaign issue for the Tories in the fortnight leading up to the vote. "We've got 15 days to overturn Labour's majority of more than 7000.

"Obviously it's going to be a tall order but we are going to give it our best shot," he said. "People in Crewe know that the more of them that vote Conservative on May 22, the clearer the message will be to Gordon Brown to do more to help those who have suffered from the tax con Budget."

Mr Cameron warned that a Labour victory at Crewe would allow Mr Brown to tell Labour rebel MPs to "get lost" but he failed to detail how his party would compensate the millions of low earners when he was challenged to reinstate the 10p rate by a voter in Crewe.

While the Tory leader on the electoral battleground was dubbing himself as a champion of the poor, Gordon Brown was left appealing to world business leaders in London on one of his passions, the campaign for international poverty relief.

Mr Brown told a meeting of 80 high-powered chief executives that the international community was in danger of missing the Millennium Development Goals of reducing infant mortality by two-thirds.

Traditionally, the Prime Minister does not campaign directly in by-elections although Tony Blair abandoned the convention first in the Hamilton South constituency in 1999.

Justice Secretary Jack Straw was on the stump for Labour in Crewe yesterday claiming that the 10p tax issue was "being dealt with" but Labour's message was drowned out by criticism from its own MPs.

Alistair Darling, the Chancellor, met with Frank Field and former whip Greg Pope, the back-bench rebel leaders over the 10p tax row, and promised a "robust solution".

Mr Field has warned again that MPs are prepared to vote down the Budget unless the package is backdated to April when the changes came in.

Then the Former Home Secretary Charles Clarke weighed in with advice to abandon proposals for 42-day detention without charge of terrorist suspects.

The government faces defeat by backbench rebels on the issue but Mr Brown is determined to be seen as tough on terrorism.

In a magazine article Mr Clarke outlined a recovery programme including a "mini-Budget" to establish a clear sense of political direction and strengthen economic confidence after the tax rate debacle.

Earlier Mr Brown chaired a political Cabinet, which deals entirely with party rather than government business, to plan Labour's resurrection strategy centred around draft legislation foreshadowing the Queen's Speech in the autumn.