David Davis has pulled out of the Tory leadership contest and says the race is now too close to call.

The decision came after he secured fourth place in the re-run first round of MPs votes in the contest, where he scored just one vote more than Michael Ancram who came last.

First round re-run

Michael Portillo - 50 votes Iain Duncan Smith - 42 votes Ken Clarke - 39 votes David Davis - 18 votes Michael Ancram - 17 votes

Mr Davis told a media conference at Westminster: "Having taken soundings from my colleagues in the House last night it is clear that we cannot close the gap with the next contender in the leadership election."

And as MPs faced a new wave of bids for their votes, Mr Davis announced he would now be backing Iain Duncan Smith.

Backing Duncan Smith

Mr Davis said the shadow defence secretary was the man "most likely to carry forward the agenda that we have set out in this campaign".

"I recommend my team to do the same but those of you who know my team know none of them take orders," he added.

Iain Duncan Smith: Winning new backers

His withdrawal means the 166 Tory MPs will on Tuesday select the two contenders who will go to a ballot of the party's 300,000 members.

There is now likely to be a scramble for those votes that went to Mr Davis and Mr Ancram - although the former's decision to back Mr Duncan Smith will be a blow to both the Clarke and Portillo camps.

Later, Mr Davis told BBC News the final MPs vote would go "right to the wire" with only one vote deciding whether Mr Portillo or Mr Clarke won the vital second place behind Mr Duncan Smith.

With another round to go, Mr Duncan Smith said he was taking nothing for granted.

"We have to fight to persuade colleagues that I'm the one they should choose," he told BBC News.

Crossing camps

Eric Forth was the first Davis supporter to say he too would support Mr Duncan Smith and he predicted "a significant proportion" of his fellow Davis supporters would join him, with the rest turning to Ken Clarke.

The former chancellor himself predicted he would get a good number of Davis votes and more from former supporters of Michael Ancram.

"I know perfectly well lots of David Davis voters are going to vote for me," said Mr Clarke, insisting he was on course to come second next week.

Mr Clarke is confident he can win second place

He praised Mr Davis's campaign, adding: "David Davis is going to be a very big man in the Conservative Party."

All eyes now will be on Michael Ancram, who was automatically eliminated on Thursday when he came last in the re-run first round.

He said he would be thinking about which candidate was most likely to achieve his chief aim - party unity.

Early frontrunner Michael Portillo topped Thursday's poll of MPs but added only one vote to his tally in the first ballot on Tuesday.

Mr Portillo's failure to pick up more than one extra vote since Tuesday's ballot prompted claims that his campaign had lost momentum.

Getting serious

But on Friday afternoon, Mr Portillo said MPs were more likely to back him as their final choice approached.

Portillo says he can end Tory divisions

"This is now serious," he told reporters.

"Now I think many of those people have been thinking about this and will now want to concentrate on which candidate has the best chance of bringing the various parts of the country together.

"I believe I have the best chance. I believe I am the least factional of the candidates and we have to make factions completely a thing of the past."

The final victor in the leadership battle will not be announced until 12 September.