David Cameron has unveiled plans for a new centre-right grouping in the European Parliament - but admitted any change would not happen before 2009.
The two leaders signed a joint declaration
The Tory leader wants to cut ties with The European People's Party (EPP), which favours closer EU integration.
Mr Cameron signed a joint declaration with Czech Civic Democrat leader Mirek Topolanek proposing a new group.
It follows months of talks in which the Conservatives have been seeking to find suitable partners.
At a joint press conference with Mr Topolanek, Mr Cameron hailed the planned new group as "a strong new voice for change, optimism and hope".
He said the move fulfilled a pledge he had made during the Conservative leadership contest to leave the EPP.
But critics say Mr Cameron had promised supporters he would quit the EPP immediately if he became leader, not in three years' time.
Labour's Europe spokesman, Geoff Hoon, said: "This is a man who has said politicians should be consistent, yet the first clear promise he has made he has broken."
Mr Topolonek said he had asked Mr Cameron to postpone the setting up of a new MEPs' group until he had completed the "complex" process of forming a coalition government.
He is the Czech Republic's prime minister designate after winning the most votes in recent elections but needs to form alliances with pro-European politicians in his country's parliament.
Mr Cameron and Mr Topolanek agreed to immediately set up a new Movement for European Reform, which would engage with political parties from countries aspiring to EU membership.
The Tory leader said that neither party could continue within the EPP for the long-term.
"While we agree about open markets and deregulation, we don't share their views about the future development of Europe," Mr Cameron said.
The new alliance planned for 2009 would be less centralised and more outward-looking, he added, and hoped to attract other like-minded parties.
Under EU rules there must be parties from at least five countries to form a Parliamentary group.
But there were signs the three year delay threatens to re-open Conservative divisions on Europe.
Shadow foreign secretary William Hague said the 26 Conservative MEPs would sit with the EPP group for the next three years - and any who attempted to leave would not be picked as Tory candidates for re-election in 2009.
He denied Mr Cameron had been "rash" when he promised, in December, to withdraw from the EPP within "months not years", arguing the "facts on the ground" had since changed.
"The Czechs, our closest allies, said, 'please wait for us, so that we can come with you'," he told BBC Radio 4's The World at One.
But Tory MEP Caroline Jackson said Mr Cameron had been "very unwise to make a pledge on something on which he didn't know the details".
She said Tory MEPs were "in for a very worrying three years".
"It's rather like saying to someone, 'I am going to divorce you, but I am going to live in the same house as you for the next three years and I am going to share the kitchen'."
The Conservatives' influence in Strasbourg would be "zero", she added, and she criticised Mr Cameron for not making the effort to meet his MEPs.
Eurosceptic Conservative MP Douglas Carswell, who said quitting the EPP was one of the reasons he voted for Mr Cameron in last year's leadership contest, said he was "a bit disappointed" by the delay.
"I wish we were coming out today," he said.
He said he would back any Tory MEP who wanted to leave the EPP now, saying such a move would be "wonderful".
Nigel Farage, leader of the UK Independence Party's MEPs, said the delay confirmed Mr Cameron's "glibness and lack of substance" and said it had "cut adrift" half of the Tory MEPs.
"Pledging to withdraw from the EPP was clearly nothing more than a sharp PR move by someone whom the term 'slick' could have been invented to describe.
"It was this, his sole promise, which gained him the leadership of his party," said Mr Farage.
He added: "Tory MEPs who wish to sit in a genuine eurosceptic group will be welcomed within the Independence and Democracy group alongside UKIP MEPs."