Paul Nuttall has hit out at Ukip quitter Douglas Carswell as a "staunch Tory" after reportedly only finding out about the MP's blog post resignation in a text from a friend.
Mr Carswell, who won back his Conservative seat for Ukip in 2014, is facing calls to trigger a by-election after plunging the party into fresh turmoil.
The Brexit-supporting MP insisted he does not need to call a fresh vote because he is not rejoining the Conservatives or switching allegiances to another party.
But Ukip's biggest financial backer, Arron Banks, has urged the MP to call a by-election in his Clacton constituency so he can stand against him.
Writing in the Telegraph, Mr Nuttall said: "Over the last year it has become clear that he has been drifting in one direction while Ukip has been marching in another.
"He has always been and always will be at heart a Brexit supporting staunch Tory, and with the referendum result sorted he has no reason to stay in a party that is moving into Labour’s turf rather than going in a direction that would make him feel more at home."
Mr Farage, who had recently called on the party to kick out the "Tory Party posh boy", said the MP "jumped before he was pushed".
The MP's resignation is understood to have come before a planned meeting with Ukip's national executive on Monday over whether he played a role in blocking a knighthood for Mr Farage.
Mr Carswell said he was resigning as the party had achieved its founding goal of getting Britain out of the European Union.