Iain Duncan Smith has defended his leadership amid renewed criticism of his judgement and ability.

As the party unveils its pension and health plans at its annual conference, the Tory leader is seeking to face down those plotting to oust him as leader.

Speaking to Sky News the Conservative leader said he wanted to offer a "real deal" to voters.

"That is what this week is about, and I tell you after the end of this week I am going on a campaign to take that to the British people, to tell them, you have had enough of lies and deceit from Tony Blair and Gordon Brown, you want the real deal, the deal that gives people at last that fairness and we are going to deliver it," he said.

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

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

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

He threatened to sue for libel against any organisation which published the charges.

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

Newspapers reported that the BBC's Newsnight programme pulled out of broadcasting the claim that he employed his wife Betsy in his office for several months after he became Conservative Party leader - even though he had access to party staff.

A report by veteran investigative reporter Michael Crick was due to aired last week but was later withdrawn, the Sunday Times and Sunday Telegraph wrote.

Duncan Smith 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".

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.