Tory MP Andrew Bridgen says a former colleague has made a big mistake by defecting to UKIP.
Mr Bridgen, MP for North West Leicestershire, said Clacton MP Douglas Carswell had told him he was worried about the level of support for UKIP in his constituency before he left the Conservatives and joined Nigel Farage's party.
Mr Bridgen said: "It's counter-productive. Douglas may have made a big mistake.
"He has always said he was concerned by the popularity of UKIP in Clacton.
"It has a demographic that suits UKIP.
"It will be a challenge for Nigel Farage. UKIP is a one-man-band and he will not be used to having someone as intelligent and independently minded as Douglas in his party."
Mr Carswell has stood down, triggering a by-election .
Senior UKIP figures have suggested other Tory MPs will follow Mr Carswell into their ranks because they are concerned about David Cameron's stewardship of the party.
Mr Bridgen, a Eurosceptic MP who has rebelled against the Government and previously openly questioned David Cameron's leadership, said he would not be joining UKIP and had not been approached by anyone from the party.
He warned Conservative supporters moving to UKIP in May's General Election would open the door to Number 10 to Labour leader Ed Miliband.
