By William James
LONDON (Reuters) - Outgoing EU Commission President Jose Manuel Barroso on Sunday warned British Prime Minister David Cameron against trying to rewrite the European Union's freedom of movement principle, saying it was essential to the bloc's internal market.
Barroso's comments to the BBC will deal a blow to Cameron's efforts ahead of a 2015 national election to appease voters who worry Britain is suffering economically and culturally because immigration is too high.
His Conservative party has suffered two high-profile defections in recent weeks to the anti-EU UK Independence Party (UKIP), which also won its first elected seat in parliament earlier this month. UKIP want an end to what they call "open-door" immigration.
"The freedom of movement is a very important principle in the internal market," Barroso said in an interview on BBC television.
"My strong advice to Britain is not to put that in question, that principle."
Writing in the Sunday Telegraph, Cameron said on Sunday that he was "putting EU migration right at the heart of our negotiations in Europe."
Cameron has broadly outlined which reforms he wants to win from the EU, such as retaining lawmaking powers at a national level, cutting red-tape for businesses and migration controls, but has not given specific details.
The Times newspaper, citing unnamed sources, on Sunday reported that Cameron wanted to cap the number of low-skilled migrants from within the EU who could register to work in the country.
When asked about such a cap in his BBC interview, Barroso said it would probably breach EU regulations and said he was not aware of a concrete proposal on the issue having been made by Britain.
"Any kind of arbitrary cap seems to me to be not in conformity with European laws," he said.
Other European leaders have expressed little appetite for revising the bloc's founding treaties but Cameron's stance on immigration and the EU has toughened in recent days as he faces another interim election on Nov. 20 triggered by the defection of one of his lawmakers to UKIP.
On Thursday Cameron, who has long said he would like Britain to stay in a reformed EU, struck a newly eurosceptic note, warning that his renegotiation attempt would be his last, and acknowledging that it might end in failure.
(Editing by Raissa Kasolowsky)