Islamophobic incidents rose by 375 per cent in the week after Boris Johnson compared veiled Muslim women to “letterboxes”, research has shown.

Monitoring group Tell Mama said the Daily Telegraph column written by the now-prime minister was followed by the biggest spike in anti-Muslim hatred in 2018, as his words were repeated by racists abusing Muslims on the street and online.

In the three weeks after the article was published last August, 42 per cent of offline Islamophobic incidents reported “directly referenced Boris Johnson and/or the language used in his column”, a report said.

Many were directed at visibly Muslim women who wore the niqab or other veils, who were called “letterboxes” and “ninjas”.

Online abuse reported to Tell Mama repeated the same words or incorporated them into pictures and memes that were sent to Muslims online.

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“Mr Johnson faced no punitive action from the Conservative Party and many high-profile figures offered their support for his right to freely speak about Islamic clothing,” Tell Mama said.

“Some will feel emboldened by the lack of sufficient castigation from the Conservative Party towards Mr Johnson and will use it as a pretext to act on their underlying prejudices and racist views.

“The consequent rise in anti-Muslim attacks, focusing on the same victims and using the same language, shows us that those with anti-Muslim sentiments feel confident and vindicated.”

Tell Mama’s research shows Muslim women already endure the highest levels of Islamophobic hatred and make up the majority of victims, while most known perpetrators are white men.

The organisation’s annual report, entitled Normalising Hate, said some politicians had defended Mr Johnson and suggested a “distressing willingness of some MPs to stir anti-Muslim sentiments because they regard it as a vote-winning strategy”.

Dawn Butler, Labour’s shadow equalities secretary, called the figures “chilling”.

“The fact that this same MP is now the prime minister is stomach-turning and shames our country,” she added.

“Mr Johnson’s bigotry has resulted in attacks on Muslim women and his refusal to apologise for his hateful remarks has emboldened racists and the far right.

“He actively fans the flames of hatred and division. His words have damaging consequences. He is not fit to sit in the House of Commons, let alone No 10.”

The graph shows a spike in racist attacks in the wake of the now prime minister’s column last summer (Tell Mama)

In December, Mr Johnson was cleared of breaching the Conservative Party’s code of conduct after an independent panel decided the former foreign secretary was “respectful and tolerant” and was entitled to use “satire” in his newspaper column.

Mr Johnson had said full-face veils should not be banned, but it was “absolutely ridiculous” women chose to “go around looking like letterboxes” and “bank robbers”.

He later defended his words, insisting the backlash against them was nothing more than “confected indignation” at his “strong views” on Brexit.

The EU referendum was followed by a wave of anti-Muslim hate crime in 2016, while Isis-inspired terror attacks acted as “trigger events” in 2017, Tell Mama said.

“Now we are seeing attacks inspired and influenced by other anti-Muslim attacks,” the report added.

It said “Punish a Muslim Day” letters sent across the UK in March also caused a spike in incidents, as well as grooming gang cases, Donald Trump’s visit and debates around the refugee crisis and Windrush.

Tell Mama found the US president’s attacks on Sadiq Khan, the mayor of London, and wider statements on Islam “have triggered further harmful debates about Muslims in Britain”.

The report warned of the impact of conspiracy theories including the “great replacement”, which was cited by the Christchurch shooter and other far-right terrorists as a key motivation.

It said the growth of hyper-partisan alternative news platforms, including several websites supporting Tommy Robinson, were spreading anti-Muslim hatred and falsehoods.

Religious hate crime rises 40% in England and Wales - with more than half directed at Muslims

In total, Tell Mama received 2,963 reports of anti-Muslim hate incidents in 2018. It took 1,072 verified reports, of which 70 per cent happened on the street and 30 per cent online.

The group received reports of a further 1,891 anti-Muslim hate crimes and incidents through data-sharing agreements with 20 police forces in the UK.

Robert Jenrick, the communities secretary, said: “I am utterly appalled by hatred aimed at Muslims in Britain or at those of any faith, and I am determined to tackle it.

“We have put millions into protecting all places of worship and we continue to fund education courses to tackle this scourge at its root. While it is welcome to see that reported incidents of abuse online and on our streets has fallen, it’s clear that there is more to do.