LONDON (BLOOMBERG) - Theresa May piled pressure on her former foreign secretary Boris Johnson to apologise after he said the Muslim burqa, worn to conceal a woman's face and body, made wearers look like bank robbers and letter boxes.

Johnson used his weekly column in the Telegraph newspaper on Monday to argue against a ban on the burqa, as implemented by Denmark, France and Austria, saying people should be free to choose their own dress.

But he mocked the garment, saying it was "absolutely ridiculous that people should choose to go around looking like letter boxes," and that face coverings made the wearer resemble a "bank robber."

"Women should have the freedom to choose how they dress," May told reporters in Scotland on Tuesday in comments confirmed by her office.

"It's very clear that that language that Boris used has offended people."

She stopped short of saying he should be thrown out of the Conservative Party.

Since he resigned in protest at May's Brexit plans last month, Johnson has been touted as a potential prime minister by those in the Conservative Party who want a harder departure from the European Union.

But others see his comments as an example of why he would be a poor candidate.

Conservative Party chairman Brandon Lewis said he had asked Johnson to apologize, though didn't say if there would be any sanctions if the request was ignored.

Foreign Office Minister Alistair Burt said Johnson's comments were "offensive" and former Tory chair Sayeeda Warsi said they were "crass."

" Boris knew what he was doing," Warsi told Sky News.

" Boris is making yet another leadership bid and he will say and do whatever needs to be said and done. I sincerely hope he doesn't continue to use Muslim women as a convenient political football."

Johnson declined to comment on Tuesday, but a person familiar with his views said he was speaking up for liberal values and stood by his article. In his column, Johnson wrote that it was "weird and bullying to expect women to cover their faces."