Iain Duncan Smith has warned rebel Tory MPs that they must unite behind him if the party is to be taken seriously.

The embattled Tory leader, referring to efforts to "undermine" him, told a packed press conference that the Conservatives "cannot go on in this fashion".

My message is simple and stark: unite or die Iain Duncan Smith

He was speaking after a rebellion by Tory MPs over the right of unmarried couples to adopt children.

But his appeal was rebuffed by rebels and former leadership contenders Kenneth Clarke and Michael Portillo.

They reacted angrily to accusations they had ulterior motives in defying Mr Duncan Smith on the issue of whether unmarried couples should be allowed to adopt children.

On Tuesday night, the House of Lords dropped its opposition to the change, voting by 215-184 in favour of it.

The move spares Mr Duncan Smith the potential problems which could have been caused had the issue been forced back to the Commons again.

'Unite or die'

Mr Duncan Smith had spent the morning locked in crisis talks after hastily cancelling a scheduled appearance at a press conference on housing policy with shadow deputy prime minister David Davis.

He said: "We have to pull together, or we will hang apart.

"If we are to be taken seriously as an Opposition, as an alternative government for this country, we have to work together.

Rebel Tories

John Bercow Ken Clarke David Curry Julie Kirkbride Andrew Lansley Andrew Mackay Francis Maude Michael Portillo

"I cannot allow the efforts of a dedicated team in Parliament or of hundreds of thousands of hard-working volunteers to be sabotaged by self-indulgence or indiscipline.

"The Conservative Party wants to be led. It elected me to lead it in the direction I am now going.

"It will not look kindly on people who put personal ambitions before the interests of the party.

"My message is simple and stark: unite or die."

Eight Tories - including former Conservative leadership challengers Michael Portillo and Ken Clarke - defied a Conservative three line whip (an order to vote a particular way) to back giving unmarried and gay couples the right to adopt.

Mr Portillo went further and spoke against the Conservative line on the issue - contrasting it to Mr Duncan Smith's party conference pledge to modernise the party.

Mr Portillo: Ruled himself out of leadership race

The row over the issue came as Mr Duncan Smith continued to face talk that his leadership was in crisis, with continued reports that some Tory MPs were preparing a leadership challenge.

Shadow Health Secretary Liam Fox earlier attacked the rebels' motives in "hijacking" a debate about the welfare of children "to make it about Westminster politics".

He said a group of Tory MPs were seeking to destabilise Iain Duncan Smith's leadership, whether out of "conviction, ambition or cynical self-interest".

Commenting on the furore, Labour party chairman Dr John Reid said: "It is really is quite extraordinary.

"You have a leader incapable of leading, presiding over a party that does not want to be led."

Monday night's revolt followed the earlier resignation of shadow cabinet member John Bercow, who said he felt he had to step down in principle over the adoption issue.

Mr Duncan Smith's attack on rebels, and his appeal for unity, clearly angered Mr Clarke.

He said: "It would be very much easier to unite as a party if Iain Duncan Smith would refrain from imposing three line whips on subjects which have always been left to the judgement of individual MPs.

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"I continue to be in favour of allowing heterosexual couples to adopt children after they have been vetted as suitable by the Adoption Agency and that is what last night's vote was about."

Fellow rebel MP, and another failed leadership contender, Mr Portillo, said: "I voted against a three-line whip for the first time in my life because I believed it was wrong and inconsistent to use coercion on adoption, and that was my only reason for doing so.

"I reject entirely the unwarranted misinterpretation of the motives of those tens of MPs who were unable to support the party last night."

Six shadow cabinet ministers were among the 35 Tory MPs who did not register a vote.