Nick Boles, the Tory MP for Grantham and Stamford, has resigned from his local Conservative association after public disagreements regarding his stance on Brexit.

Boles, who has represented the constituency since 2010, has been at the head of efforts in parliament to deliver a softer exit from the EU, co-sponsoring an amendment with Labour’s Yvette Cooper in January that would have given parliament control over the Brexit process.

He had been facing efforts by local activists in the Grantham and Stamford Conservative Association to dump him as the party’s candidate for the next general election.

In a letter obtained by the BBC, Boles said: “I am not willing to do what would be necessary to restore a reasonable working relationship with a group of people whose values and views are so much at odds with my own.”

He told his local party: “I regret that my relationship with you should end in this way. But a politician without principles is worthless. I am in no doubt about my duty, which is to be true to my convictions and to dedicate the rest of my time in parliament to the best interests of the people I was elected to serve.”

Boles said he would stay on as an MP and continue to take the Conservative whip at Westminster “if it is offered to me on acceptable terms”. Julian Smith, the chief whip, made it clear that Boles was a “valued member of the Conservative parliamentary party, which I hope will continue to benefit from his ideas and drive”.

A senior official at Boles’s local association, however, said they had been betrayed and called on him to take the “honourable course” and quit as an MP.

Moves to deselect Boles began in February, when his local party voted to start the process of looking for a candidate, meaning that he would have had to put himself up for reselection.

Boles has insisted that he is not in favour of derailing the Brexit process, but that he is fiercely against a no-deal exit.

“While I have consistently argued that Brexit must be delivered, and have voted for the prime minister’s deal every time she has brought it to the House of Commons, I am certain that crashing out of the EU without a deal would do great harm to the British people and have done everything in my power to prevent it,” he wrote.

Cllr Martin Hill, the vice-president of the Grantham and Stamford Conservative Association, told local party members: “As you are all aware, Nick has been at odds with the local party and the prime minister for some time, so this announcement does not come as a complete surprise, but the timing does leave at lot to be desired.

“I understand that it is Mr Boles’s intention to carry on as the MP for Grantham and Stamford until the next general election, despite being elected to represent us in parliament.”