Pudsey Conservative Association chair Jason Aldiss, a longstanding official and campaigner, tendered his resignation this morning hours before Mr Johnson travels to Buckingham Palace to be asked by the Queen to form a government.
Mr Aldiss, a successful veterinarian and businessman, had backed Jeremy Hunt – Mr Johnson’s rival – during the Tory leadership contest.
Describing Mr Johnson as “unelectable”, his resignation exposes the deep splits within the Tory ranks in one of the most marginal seats in the country.
It is currently held by Stuart Andrew, a defence minister, who backs Brexit. He also endorsed Mr Johnson in the leadership contest.
In a hard-hitting letter to Brandon Lewis, the party’s national chairman, Dr Aldiss blamed Brexit for his decision after serving his party in West Yorkshire for a quarter of a century.
“However, my love for my country vastly supersedes my loyalty to my Party. I did not believe in Brexit and campaigned against it. The narrow decision in favour of the United Kingdom’s departure from the European Union was the wrong path to tread,” he wrote.
“Theresa May’s election as Conservative Leader and Prime Minister in 2016 gave me fresh hope of something short of a catastrophic outcome. She demonstrated remarkable courage, tenacity, dignity and grace under extreme fire – often from prominent Conservative Members of Parliament.
“These were the same individuals who hounded her from office before manoeuvring Boris Johnson into position to seize her job. Yesterday’s leadership election result, which saw more than two thirds of party members vote for Mr Johnson, confirmed that this is no longer the party I joined in 1995
“The hardline Brexiteers in Conservative ranks, hellbent on a no-deal departure, claim to be patriots. I see nothing patriotic about willingly risking untold damage to our economy, to jobs and to our global standing for decades to come.
“They also claim to be Unionists but, through their actions, they have placed the future of the Union itself in grave peril. It may already be too late.
He added: “The election of Boris Johnson as the new Prime Minister and self-styled Brexiteer-in-chief is surely the final insult.
“Mr Johnson and his band of power-hungry saboteurs in the Parliamentary Party claim he is the only Conservative who can keep Jeremy Corbyn out of Downing Street. I wholeheartedly disagree.
“Mr Corbyn is indeed a danger to our country. He is also unelectable. I would say precisely the same about Mr Johnson.
“The country desperately needs a credible Conservative Prime Minister leading a functional Government in the interest of the entire United Kingdom. By electing Mr Johnson, the Party has effectively given up on Scotland, handed swathes of seats to the Liberal Democrats in the south of England and left moderate Tory voters in the north of England feeling disenfranchised.
“Unlike some very senior Conservatives who have buried their true feelings in the hope of preferment under Prime Minister Johnson, I can no longer defend this misguided, dysfunctional, disingenuous obliteration of years of hard work.
“I am left with no option but to resign.”
In a tribute, Mr Andrew told The Yorkshire Post: “I would like to thank Jason for all the work he has done for the party and for me personally.
“The leadership election was a major democratic process for the party and two thirds elected Boris to be our leader. Everyone else I have spoken to has said that now is the time to unite and get on with the job of government and that is precisely what I intend to do.”
Meanwhile Jane Aitchison, Labour’s official candidate for Pudsey for the next election, warned that a Johnson government and hard Brexit will be bad news for Leeds and the North.
She said: “A Tory party chairman resigning in protest at their choice of prime minister is a damning indictment of the threat Boris Johnson poses to our country.
“With the backing of Pudsey MP Stuart Andrew, Boris Johnson has become prime minister by promising tax cuts for the richest, presenting himself as the bankers’ best friend, and pushing for a damaging No Deal Brexit.
“Their no-deal would mean job cuts, higher prices in the shops, and risk our NHS being sold off to US corporations in a sweetheart deal with Donald Trump.
“The Tories think Johnson will let down the country and in supporting him Stuart Andrew has let down the people of Pudsey.”
But former Leeds North East MP Timothy Kirkhope expressed disappointment that Mr Aldiss had left the party.
Now a Tory peer, he tweeted: “I am very sorry to hear this. Jason has been one of the most diligent Conservative Members in our region for many years. I, personally, have benefitted from his experience and wisdom on a number of occasions.”