Conservative MP Nick Boles is resigning from his local party, he has told his local Tory association.
Mr Boles intends to remain as MP for Grantham and Stamford.
He has spoken out against the UK leaving the EU without a deal and has faced calls for his deselection over his Brexit stance.
In his letter, seen by the BBC, he said he was resigning with immediate effect and that a “division had opened up” between him and the local association.
He wrote: “I regret that my relationship with you should end in this way. But a politician without principles is worthless.”
Councillor Martin Hill, vice president of the Grantham and Stamford Conserva