Bromley and Chislehurst MP Bob Neill says former Tory MP Douglas Carswell’s defection to Ukip is “misguided” and “self-defeating”.
Mr Neill joined many other Conservatives in saying Mr Carswell would have contributed more to the European Union debate had he stayed loyal.
The past member for Clacton yesterday (Aug 28) caused shockwaves in British politics when he resigned his seat and joined Ukip. He will now fight a by-election.
Mr Neill told News Shopper: “I think it’s seriously misguided of him to have done what he’s done.
“I know him and get on well with him – I think it’s important to work as part of a team. It’s self-defeating.
“I think he’s let the side down”.
Mr Neill added it would have been far better if his former colleague had stayed - as the Conservatives are the “only party able to offer an EU referendum”.
He added: “It’s such a shame – we’re working towards a referendum. It’s important to support the vote.
“We want to make sure we don’t end up with a Labour or Liberal Democrat government.”
The Bromley MP, who describes himself "a moderate Tory, conceded he is a “bit of a Eurosceptic” and “radical reform is needed”.
But Mr Carswell clearly holds stronger views on Europe and claimed yesterday that Prime Minister David Cameron “is not serious about the change we need”.
He said only UKIP could "shake up that cosy little clique called Westminster".
Mr Cameron pledged an ‘in/out’ referendum in 2017 and yesterday commented on Mr Carswell’s decision to jump ship, calling it “regrettable” and “counterproductive”.
If Mr Carswell gains support from voters he will be the first Ukip MP elected in the Commons.
The move was welcomed by Ukip leader Nigel Farage, who said more defections are likely if his new candidate wins Clacton back.
It comes amid claims the Conservatives are worried about the Ukip threat with the 2015 General Election drawing near.
But Mr Neill, who is set to contest his Tory stronghold seat next year, said he is not concerned.
He added: “I’ll be fighting to regain my seat. The job is not done and I hope people give us the time to do it.
“You can never place them (Ukip). But I don’t want to give them a chance.”