Cameron vows to fight for NHS as parties gear up for early election

In an attempt to claim the centre ground ahead of a possible autumn election, the Tory leader will warn that 40 maternity units and 90 A&E units are under threat of closure.

He will also seize on suggestions from Lord Darzi, who is heading a major health review for the Government, that many district hospitals should close.

Lord Darzi says Britain needed "fewer, more advanced and more specialised hospitals".

Mr Cameron's switch to health issues will risk complaints that he is returning to a "soft" agenda after delighting the Tory Right with proposals to scrap inheritance tax.

The tax-cutting plans, drawn up by John Redwood, have been welcomed by George Osborne.

The Shadow Chancellor warned, however, that any cuts would be paid for by higher taxes on car and air travel.

Mr Osborne made clear his party would make a manifesto promise to scrap death duties.

He wrote in the Mail on Sunday: "I understand how inheritance tax is fast becoming an unfair tax in aspiration.

"I want to make sure that the next Conservative government is ready to help the millions of families striving hard to provide a better life for their children and who have had such a raw deal from this Labour Government."

Tory defence spokesman Liam Fox told BBC News 24 tax "would be a great issue for us to raise at the general election".

Labour and Tory MPs have already been put on poll alert by their party headquarters.

A leaked memo from Conservative chairman Caroline Spelman, headed "General election preparations", orders activists to gear up for a campaign this autumn.

The document, leaked to the Sunday Telegraph and dated August 17, says an election "could be called at any time from the beginning of September".

It adds: "George Osborne has chaired the first meetings of our general election planning team which continues to meet through August.

"Work has commenced on developing a manifesto."

Tory figures suspect Mr Brown may risk an early election after establishing a ten-point poll lead.

According to the Observer, the Prime Minister will decide in the first ten days of September on whether to gamble on going to the polls.

He received a boost when it emerged that Unite, Britain's largest union, has set aside £26million for a campaign.

The cash had been kept in reserve until Tony Blair's resignation.

Labour has debts of £24million.