Boris Johnson has been compared to Adolf Hitler by the leader of a Conservative Muslim Forum.
Mohammed Amin, chairman of the forum, said he would quit the Conservative Party after more than three decades as a member if Mr Johnson was chosen as the next Tory leader.
His comments come after the former Foreign Secretary became the frontrunner in the Conservative leadership race, winning the backing of 114 MPs.
Asked about Mr Johnson’s popularity, Mr Amin told BBC Radio 4’s Today programme: “There are many horrible people who have been popular. Popularity is not the test. The test is, is this person sufficiently moral to be prime minister, and I believe he fails that test.”
He added: “A lot of Germans thought that Hitler was the right man for them.”
When it was put to him that such a comparison was shocking, Mr Amin said: “Yes. I am not saying Boris Johnson wants to send people to the gas chamber, clearly he doesn’t. He’s a buffoon.
“But he, as far as I’m concerned, has insufficient concern about the nature of truth for me to ever be a member of a party that he leads.”
He said: “I am not prepared to be a member of a party that chooses him as its leader. I would resign after 36 years.”
Mr Amin went on: “We don’t expect our politicians, our prime ministers, to be saints. But we do require a basic level of morality and integrity.
“And of all the candidates in the Conservative Party leadership election, Boris Johnson is the only one that I believe fails that test.”
Mr Amin said a column Mr Johnson wrote last August which compared women who wore burkas to “letter boxes and bank robbers” had put some Muslim women at risk.
“He knew exactly what effect it would have,” he said. “It would lead to Muslim women who wear niqab and burka being verbally abused on the streets; in certain cases being physically assaulted, with people trying to tear it off.
“He chose to mock Muslim women who wear niqab and burka for his own purposes.”