A Liberal Democrat MEP has defected to the Conservatives, saying the Lib Dems had "lost their way".
Sajjad Karim, MEP for the North West of England, said he had been impressed by David Cameron's speech on immigration.
Asked why he had left now, during a Lib Dem leadership race, he said it was not a "snapshot decision" but one he had been thinking about for some time.
But the Lib Dems said they believed it was because he was disappointed to be selected second on their MEP list.
The 37-year-old former solicitor was elected to the European Parliament in 2004 and says he had been with the Lib Dems for 18 years.
'Rational and positive'
He said he had been waiting to see if Mr Cameron could change his party as he saw himself as a "Liberal Conservative".
"David Cameron's recent speech on immigration was incredibly impressive - sensible, rational and positive," he said.
"It persuaded me that he is a leader who has changed his party and will change this country.
"I'm afraid that the Liberal Democrats have lost their way and are no longer a serious force in politics."
He was welcomed by both Mr Cameron and the leader of the Conservatives in the European Parliament Timothy Kirkhope.
"He is a hard-working MEP who has so much to offer. I look forward to working with him," Mr Cameron said.
But the Lib Dems suggested Mr Karim switched parties because he was not placed top of their list of north-west candidates for the next European Parliament elections in 2009.
A spokesman said: "We are saddened that Saj Karim has decided to leave the Liberal Democrats following the results of the selection process for the North West region of the European Parliament.
"Although Saj was elected in second place on the Liberal Democrat list for the European Parliament, we were confident that he would have secured re-election to the Parliament.
"We are sorry that his disappointment in the result has led him to switch parties."