"Boris Johnson’s comments comparing Muslim women in veils to letterboxes gave people the impression that the Conservative Party 'are insensitive to Muslim communities'..."

"... an independent report has concluded.... The review, set up in 2019 and led by psychiatrist Swaran Singh... said that 'anti-Muslim sentiment remains a problem' in the party but concluded that there was no evidence of systemic discrimination.... In a statement to the commission, Johnson apologised for any offence caused by his letterboxes remark and said: 'I do know that offence has been taken at things I’ve said, that people expect a person in my position to get things right, but in journalism you need to use language freely. Would I use some of the offending language from my past writings today? Now that I am prime minister, I would not.' Johnson made the letterboxes comment in a Daily Telegraph column where he criticised a law passed in Denmark to ban the niqab, a full face veil with a slit for the eyes, and the burka, a full covering with a mesh over the eyes. He wrote that the law should not tell 'a free-born adult woman what she may or may not wear in a public place,' but added that it is 'absolutely ridiculous that people should choose to go around looking like letter boxes.'"

The London Times reports.

Presumably, Johnson was picturing the English-style "pillar box":

It was a rude remark. He could have been more careful. In the words of the great Englishman John Lennon: Thoughts meander like a restless wind inside a letterbox/They tumble blindly....