Iain Duncan Smith will today begin a fight for his future amid renewed criticism of his leadership.

As the party unveils its health plans, the Tory leader will seek to face down those plotting to oust him as leader.

Over the course of the weekend it was alleged that Duncan Smith was the subject of an orchestrated "smear" campaign designed to undermine his leadership.

Interviewed yesterday senior Tory MP Francis Maude conceded that the leadership was once again "an issue".

Fleet Street today suggests that Duncan Smith is still "on probation" and faces a "make or break" conference this week.

Express political editor Patrick O'Flynn goes further urging the party to "get rid of the quiet man".

Other reports suggest that Tory grandees are considering plans to hand Duncan Smith a "revolver in the library".

It is said the plotters are seeking 50 names of MPs and senior peers who will write to Duncan Smith calling for his resignation.

The Conservative leader was this weekend forced to deny claims that his office expenses were illegitimate.

Duncan Smith was responding to Sunday newspaper stories claiming that the BBC pulled out of broadcasting allegations that he was mis-using taxpayers' money.

Speaking on BBC television on Sunday, Duncan Smith said he was prepared to sue over allegations about the running of his office.

He told the Breakfast with Frost programme the claims were "false lies".

"I say categorically to you now if anybody makes such allegations... I will sue them," he said.

But this week he faces a tough fight in convincing those who doubt he has the political intelligence or charisma to make it to Number 10.

And a series of opinion polls published today make bleak reading for the Tory high command.

An NOP poll for the Independent newspaper finds that 41 per cent of voters now believe the Lib Dems to be the "real opposition" - and finds that nearly half of all voters cannot name the Tory leader.

Meanwhile a Populus poll for the Times finds that the Tories remain on 31 per cent - five points behind Labour and just five points ahead of Charles Kennedy's party.

A YouGov poll for the Telegraph leads the paper to suggest Duncan Smith is "running on the spot".