Boris Johnson’s suggestion that burka-wearing women look like “letterboxes” and “bank robbers” gave an impression that the Tories are “insensitive” to Muslims, an inquiry into Islamophobia in the party has said.

In a pointed message to the prime minister, the review led by professor Swaran Singh said the leadership of the Conservative Party “ought to set a good example for appropriate behaviours and language”.

Tory chair Amanda Milling said the Conservative Party accepted the recommendations of the report and apologised “to anyone who has been hurt by discriminatory behaviour of others or failed by our system”.

The report said high profile cases such as Johnson’s and the controversial London mayoral campaign run by Zac Goldsmith against Sadiq Khan in 2016, during which the Tory accused his Muslim Labour rival of associating with extremists, “give the impression to many that the party and its leadership are insensitive to Muslim communities”.

The inquiry found anti-Muslim sentiment was seen at local party association and individual levels but claims of “institutional racism” were not borne out by evidence of the way complaints were handled.

But it acknowledged that “anti-Muslim sentiment remains a problem” within the Tory Party, while Singh said the report should make “uncomfortable reading”.

“While the party leadership claims a ‘zero tolerance approach’ to all forms of discrimination, our findings show that discriminatory behaviours occur, especially in relation to people of Islamic faith,” the report said.

Labour said the report was a “damning indictment of the discrimination rife in the Conservative Party” and demanded an apology from Johnson.

The prime minister was cleared by a majority on an independent panel over a complaint he broke the party’s code of conduct following a Daily Telegraph column in 2018 which described Muslim women who wear the burka as looking like “letterboxes” and “bank robbers”.

Johnson said he was “sorry for any offence taken” over his journalism and told Prof Singh’s investigation: “Would I use some of the offending language from my past writings today? Now that I am prime minister, I would not.”

The Singh Investigation report said several interviewees who spoke to the inquiry considered Johnson’s language “discriminatory and unacceptable”.

In response to Johnson’s assertion he would not make such remarks now, the report said: “While this could be considered leading by example, the investigation would like to emphasise that using measured and appropriate language should not be a requirement solely for senior people, but ought to be expected throughout the Conservative Party.”

The report said Goldsmith “accepts poor judgement in the way his campaign was conducted but forcefully denies harbouring anti-Muslim sentiments or using such sentiments for political advantage”.

But Singh told the PA news agency: “I’m not saying that the party leadership is insensitive to Muslim communities.

“I’m saying that the perception is very strong.”

From 2015-2020 the party’s central database recorded 1,418 complaints relating to 727 incidents of alleged discrimination – an average of 237 complaints about 122 incidents a year in a party of 200,000 members.

More than two-thirds of the incidents – 496 cases – related to Islam and 74% of all the cases involved social media activity.

Around a third of cases – 231 – resulted in a sanction, with 50% resulting in a suspension and 29% an expulsion from the party.

No action was taken in 418 incidents for reasons including the complaint being in relation to someone who was not a party member, insufficient evidence or a prior investigation.

There was no evidence that complaints related to Islam are treated differently from those related to other forms of discrimination, nor did the panel find evidence of attempts to pressure or interfere with the handling of individual complaints.

But Singh told PA the complaints process was “clunky, cumbersome and slow, and not transparent”.

The review process has been regarded with scepticism by some critics, with the Muslim Council of Britain warning it would be a whitewash.

But Singh said: “I hope fair minded people who read the report will see that we haven’t shied away from criticising the party.

“In fact, this is going to be very uncomfortable for the party, I hope it makes them uncomfortable, I hope it makes the rank and file uncomfortable and it also spurs them into action.”

In a message to Johnson, Singh said: “As the leader of the Conservative Party, I would say lead by example and accept our recommendations unequivocally. Accept them unconditionally. Implement them and get someone to monitor the implementation.”

The report called on the Tories to introduce sweeping changes to the complaints process, publishing an action plan within six weeks to set out how it will respond, followed by a six-month progress report and a one-year review carried out by an appropriate body.

Within six weeks, the party should review its social media rules and within six months develop training on “acceptable” behaviour online.

Within a year, the report said the party should produce and implement a single, mandatory code of conduct across the entire membership in England, Wales and Northern Ireland.

Labour’s shadow equalities secretary Marsha de Cordova said: “This report is a damning indictment of the discrimination rife in the Conservative Party, and it goes all the way up to the prime minister.

“Reports of Islamophobic hate crime spiralled in the weeks after Boris Johnson likened women who wear the burka to ‘letterboxes’ and ‘bank robbers’.

“He must now issue a full and proper public apology that acknowledges the pain and hurt he has caused in the Muslim community, as well as taking meaningful action to rebuild trust, especially among Muslim women.”

A spokesperson from the Equality and Human Rights Commission said: “We are pleased to see that the independent investigation has now published its report.

“We have been kept informed of the progress of the investigation by Professor Singh and will evaluate his team’s findings carefully. 

“We will assess the report alongside the investigation’s terms of reference and await the Conservative Party’s response on the actions they will take. This process will take some time and we do not anticipate making any further comments until that work is completed.”