Horsham MP Francis Maude today became the most senior Conservative to publicly call for a vote of confidence in party leader Iain Duncan Smith.

The former shadow chancellor and shadow foreign secretary said he had written to the chairman of the powerful backbench 1922 Committee calling for a ballot.

Four other backbenchers have declared publicly they have done the same.

Mr Duncan Smith will address a meeting of the 1922 Committee tomorrow, after his demand for an end to the plotting.

It is up to committee chairman Sir Michael Spicer to call for a vote of confidence if 25 letters from Tory MPs are received.

Mr Maude told BBC Radio 4's Today programme the turmoil in his party had to be ended this week.

He said: "There has been a sense of widespread discontent and concern and it really has to be brought to a head one way or the other. We can't carry on like this. This week is the week in which people either step up or shut up."

Meanwhile Ryedale MP John Greenway, who left Mr Duncan Smith's shadow cabinet in June, said: "For the sake of my party and for the sake of my country, I believe we have to have a vote of confidence."

Old Bexley and Sidcup MP Derek Conway and Reigate MP Crispin Blunt have also written to Sir Michael. A fifth said he too had added his name to the list.

But as some plotters broke cover, others spoke out in support of their leader.

Surrey East MP Peter Ainsworth said: "I entirely support Iain Duncan Smith and I share in the dismay of many thousands of Conservatives all over the country at the selfish infighting that has been taking place in recent weeks."

Mr Duncan Smith would need a majority of the votes cast by his 165 MPs to survive.

Last night he suggested he would stay even if he won a confidence vote by just one MP.