Roger Lord had been sel-ected to stand at the next general election, but was sidelined after Mr Carswell announced he was leaving the Conservative party and standing down from Parliament, forcing a by-election in Clacton, Essex.
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Mr Lord, a farmer, has now resigned from Ukip and his role as a county councillor for Brightlingsea.
He ruled out standing against Mr Carswell, but said that if rumours of further high-profile defections prove true, Ukip leaders risk changing the nature of the party.
Mr Lord added: "There are loads of good people within Ukip who have worked hard for a long time and deserve to be shown a degree of respect.
"If the leadership continues to demean those people and sweep candidates aside, it could backfire.
"I may well be just the first of many to be trampled on in this way. Voters certainly won't be impressed by people being moved around like chess pieces."
It has been claimed eight Tory MPs have "lunched" with Ukip and that euro-sceptic Labour MPs may also be considering defecting.
But Mr Lord said many existing members may dislike the approach.