TORY leader Iain Duncan Smith will today admit there is a plot to remove him by insisting he is the only person who can defeat Tony Blair at the next election.

In his speech to the Blackpool conference, Mr Duncan Smith will state that "my mission" is the only hope for Conservatives desperate to beat Labour.

Mr Duncan Smith will say: "You either want my mission, or you want Tony Blair. There is no third way."

The message will immediately be seen as an attempt to beat off critics circling in his party, amid growing rumours of a conspiracy to unseat him, perhaps within weeks.

It will be delivered amid reports that up to 15 Tory MPs have written to the chairman of the party's backbench committee, demanding a leadership ballot.

Under the party's rules, only 25 MPs are required to come forward to trigger a challenge, at which point the game will almost certainly be up for Mr Duncan Smith.

Until today, Mr Duncan Smith has attempted to brush aside any suggestions that he was about to be told his time was up.

But the chairman of one Conservative constituency party predicted the speech would need to be "an absolute barnstormer" to ward off a leadership challenge.

In his speech, Mr Duncan Smith will launch a passionate defence of the raft of new policies outlined in Blackpool this week, including higher pensions and vouchers for better education and health care.

He will insist that the Tories, who are still struggling in the polls, have a record of bouncing back to defy the pollsters by triumphing at elections.

Mr Duncan Smith will say: "Today, I stand before you with the most radical policy agenda of any party aspiring to government since 1979.

"They said we couldn't win the May elections and we did. We are the largest and fastest growing party of local government. My mission is to take the Conservative Party back to government."

Mr Duncan Smith will also launch his fiercest attack yet on the Prime Minister and warn that Labour will "play dirty" at the next election,

He will say: "A Prime Minister that lied about his own record won't hesitate to lie about us.

"A Government machine willing to smear the Paddington train crash survivors and Dr Kelly won't think twice about smearing me.

"A political party prepared to use the tragedy of September 11 to bury bad news will do everything it can to hide the scale of its own failure."

Mr Duncan Smith received a boost yesterday when Shadow Chancellor Michael Howard, who is seen as the most likely "stop-gap" successor, pledged his loyalty, describing Mr Duncan Smith as an "excellent leader".

Yesterday, asked what he would say if the 25 signatures required for a leadership contest were gathered, Mr Duncan Smith replied: "Get lost. I'm going straight to the finish and I'm going to take this party through to the general election."

More mystifyingly, when asked the same question later, he said he would reply: "Go and put them in a telephone box."