Tory leader Iain Duncan Smith today challenged warring party colleagues to "unite or die" after a Commons rebellion split MPs across Sussex.

Outside Central Office, Mr Duncan Smith accused what he called a "small group of my Parliamentary colleagues" of seeking to undermine his leadership.

A hastily-arranged lunchtime Press conference followed the debate last night, in which Sussex MP Tim Loughton came under a fierce personal attack as he tried to defend his party line against the relaxation of adoption rules.

The East Worthing and Shoreham MP was savaged by former Tory leadership contender Michael Portillo as he spoke in defence of the party's decision to impose a three-line whip - an order on how to vote - against plans to allow gay and unmarried couples to adopt.

Horsham MP Francis Maude was one of eight senior Tories who revolted against Mr Duncan Smith in the row, which many see as the foreshadowing calls for Mr Duncan Smith to step down.

A further six Shadow Cabinet ministers, including Arundel and South Downs' Howard Flight, were among the 35 Tory MPs who did not register a vote.

Other Tories who did not vote included Mid Sussex's Nicholas Soames, Bognor and Littlehampton's Nick Gibb and Chichester's Andrew Tyrie.

Earlier, leading Shadow Cabinet moderniser John Bercow had quit over the decision to deny Tory MPs a free vote, calling it an issue of conscience.

In the Commons, Mr Portillo, a close ally of former Shadow Foreign Secretary Mr Maude, turned these words against Mr Loughton, asking how he would have felt if he had been forced to give up his Front Bench job to vote with his own conscience.

Mr Portillo also turned Mr Duncan Smith's Tory conference speech in which he said Britain had moved on in the past 20 years, back on Mr Loughton.

Mr Loughton replied he believed there was no middle way and the Tories should resist adoption by unmarried and gay couples.

Married couples were likely to stay together longer than unmarried couples, he insisted.

The remaining Sussex Tory MPs - Eastbourne's Nigel Waterson, Wealden's Charles Hendry, Bexhill and Battle's Gregory Barker and Worthing West's Peter Bottomley - voted with Mr Duncan Smith.

But the proposal to extend the adoption rights to gays and unmarried couples won a 199 majority and will tonight return to the House of Lords.

Hastings Labour MP Michael Foster, joined by Hove MP Ivor Caplin and Brighton Pavilion MP David Lepper in supporting the proposals, warned children would continue to "languish in care"if adoption remained restricted to married couples.

At Central Office today, Mr Duncan Smith said: "For a few, last night's vote was not about adoption, but an attempt to challenge my mandate to lead the party. We cannot go on in this fashion.

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

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

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

Today Shadow health Secretary Liam Fox attacked rebels such as Mr Maude, accusing them of undermining Mr Duncan Smith.

He said they must ask themselves whether they were acting out of conviction or cynical self-interest.

David Gold, Tory candidate for Brighton Pavilion at the 2001 election, said: "I think a free vote would have been a good idea."