European Commission President Jose Manuel Barroso has said that he "regrets" David Cameron's decision to take the Conservatives out of the main centre-right grouping at the European Parliament.
He warned that the Tories may lose influence over the development of the European Union, which he said was largely shaped by the main "families" representing the conservative, social democrat and liberal traditions in Europe.
The Conservatives last week formally informed the chairman of the European People's Party/European Democrats (EPP-ED) that they will leave the group following Euro-elections in June to establish their own grouping.
The move fulfils a pledge made by Mr Cameron during his 2005 campaign for election as Conservative leader, when he promised to withdraw from a group which many Tories regard as too federalist and too supportive of the Lisbon Treaty.
The EPP-ED grouping includes centre-right MEPs from all EU states, including the parties of French President Nicolas Sarkozy, German Chancellor Angela Merkel and Italian Prime Minister Silvio Berlusconi, and is the largest faction in the European Parliament. MEPs from the Portuguese Social Democratic Party, of which Mr Barroso is a member, also sit with the EPP-ED family.
The Conservatives are expected to be joined in their new group by euro-sceptic parties from the Czech Republic and Poland. Labour have claimed that the Tories will find themselves marginalised in Europe as a result.
Asked about the move at a press conference following talks with Prime Minister Gordon Brown in 10 Downing Street, Mr Barroso said: "It is up to each party to decide in which European grouping it wants to sit. It is up to each party to decide, so I can't criticise a specific decision.
"But of course I regret that decision. My party is a member of the EPP and I regret this decision because in Europe (it is) the main political parties and the main political families that really shape the European agenda.
"On the Commission, we have members of the EPP, members of the socialist and social democrat family, we have members of the liberal family. As president of the commission, I am not party-orientated. I try to have a consensus approach.
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"But of course these are the most influential families in Europe, those who shape Europe. I have discussed this issue several times with David Cameron so he will not be surprised to listen to me saying that I regret that decision."
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