Johnson at centre of power struggle as polls say Labour must ditch Brown to win

The Health Secretary's relationship with the Prime Minister was said to be 'close to breaking point'.

Mr Johnson is understood to have been infuriated when embryology legislation, being piloted by his department, was pulled from the Commons agenda at the last minute last month.

Power play: Gordon Brown's fate might be sealed by Alan Johnson's next move

Downing Street was apparently worried about its effect on the Roman Catholic vote in the Glasgow East by- election, which Labour went on to lose anyway.

Though Mr Johnson's office insisted last night the two men had not fallen out, Mr Brown's allies are increasingly concerned at his failure to speak out in support of the Prime Minister.

The Daily Mail revealed last month that senior Labour figures wanted Mr Johnson to join forces with Foreign Secretary David Miliband to form a 'dream ticket' in a leadership race.

Mr Miliband made clear his ambitions for the top job ten days ago when he unveiled a personal manifesto for taking on the Tories, making no mention of Mr Brown.

The charismatic Mr Johnson is widely admired by Labour MPs and in the trade union movement and his support could prove crucial in any contest  -  or provide a platform for his own leadership bid.

Mr Miliband and Mr Brown are likely to be pitched into a tussle for the Health Secretary's affections.

Mr Brown may be tempted to try to bind in Mr Johnson by promoting him, possibly to Deputy Prime Minster, in an expected Cabinet reshuffle.

It emerged yesterday that union bosses hostile to the Blairite Mr Miliband are discussing the possibility of Mr Johnson taking the top job, with backbench MP Jon Cruddas as his deputy.

They believe the Health Secretary would garner more support for the leadership than Mr Miliband.

He won the backing of 90 MPs in last year's contest for deputy Labour leader. But Mr Johnson has said publicly that he does not feel up to the job of being Prime Minister, remarks that some MPs fear would be a millstone round his neck.

He looks more likely to become Labour's 'kingmaker', either swinging the party behind Mr Brown or forging an alliance with Mr Miliband.

A spokesman for Mr Johnson dismissed reports that he and Mr Brown had had a blazing row.

'He spoke to the Prime Minister about the Embryology Bill and there is no bad feeling between them,' he said.

Mr Brown's relations with Chancellor Alistair Darling, a longstanding ally, are also under severe strain.

Treasury sources suspect that Downing Street, desperate for some good news to lift the Prime Minister's fortunes, encouraged newspapers to report that the Government would help first-time buyers by announcing a 'stamp duty holiday'.

Mr Darling has been widely criticised over the stamp duty speculation, which is causing potential homebuyers to pull out of deals in the hope of saving thousands of pounds in a few months' time.

But officials say there is conflicting evidence on whether a temporary stamp duty cut would in fact do anything to help the housing market.

Labour MP and former Minister Frank Field expressed incredulity that speculation over stamp duty had been allowed to run riot. 'The outcome is pretty catastrophic, both on the impact on the economy and on the standing of the Government,' he said.

The latest YouGov survey, for yesterday's News of the World, puts the Tories 20 points ahead of Labour, on 46 per cent to 26 per cent.

But it also suggests Labour would do better without Mr Brown at the helm. More than a fifth of voters  -  21 per cent  -  said they would be more likely to vote Labour if Mr Brown was ditched.