Leading United Synagogue rabbis have expressed their concerns over Boris Johnson’s mocking of Muslim women who wear the niqab — and warned of increasing flirtation with political extremism.

In his Daily Telegraph column, the former foreign secretary likened women wearing face-coverings to “letter boxes” and “bank robbers” and described them as “weird” and “ridiculous”, triggering huge outrage, with Mr Johnson’s critics accusing him of dog-whistle racism.

Rabbi David Mason, minister of Muswell Hill Synagogue, claimed it was an example of “racism with a smile”, telling the JC the comments were “very problematic and raise a big concern”.

He also condemned members of the Jewish community who expressed solidarity with far-right sentiments on social media.

“As the Jewish community is facing antisemitism from the far left, we have to be clear about what we see on the right as well. One thing I worry about — and I see a lot of it on social media — is too many Jewish people who are sympathetic to those on the more extreme right,” he said.

“If we saw people arguing against Judaism in the way we see those on the right argue against Islam, we would have a problem with it. Wherever we see Islamophobia we need to stand up against it.”

Rabbi Moshe Freedman of the New West End Synagogue echoed Rabbi Mason, saying: “When I see people in the Jewish community siding with the far right groups or ideologies, it suggests they have completely forgotten that extreme political movements have been highly damaging to minority groups.

“We may have political disagreements with some in the Muslim community, but that shouldn’t be the green light to side with people whose ideas are odious and are threatening to us too.

“You see the same kind of intolerance focused on the Jewish community — we know what it’s like.

“The Jewish community and religious leaders should be concerned about the language used by our politicians. It’s a worrying trend and it could affect us as well.”

Yisroel Yaakov Lichtenstein, head of the Federation of Synagogues, called Mr Johnson’s column “insulting and offensive”, urging him to apologise for “aggravating people”.

But Rabbi Barry Marcus, of London’s Central Synagogue, disagreed, calling the row a “storm in a teacup”.

He said: “We can be vigilant about subversion or distortion of history, and Holocaust denial or revisionism. What Ken Livingstone said about Hitler supporting Zionism — that demanded a response.

“But what you need to be vigilant about is not people’s opinions. You can’t legislate for what people think or feel. The only thing to do is educate, educate, educate.”

Other leading figures in the Jewish community also condemned Mr Johnson’s comments, including Jonathan Goldstein, chairman of the Jewish Leadership Council, who said his remarks were “totally disgraceful”.

Adrian Cohen, chairman of the London Jewish Forum, added: “We all lose when irrational bigotry and fear are stimulated by those from the mainstream of British politics.”

Mr Johnson has so far refused to apologise for his comments, despite calls from senior Conservative Party figures to do so.