Boris Johnson has stood by his remarks about the burka after the Conservative Party chairman told him to apologise.
The former foreign secretary has been criticised for saying Muslim women wearing burkas “look like letter boxes” and comparing them to “bank robbers”.
His remarks have been branded “offensive” and “deliberately provocative”.
But a source close to Mr Johnson said: “It is ridiculous that these views are being attacked.”
“We must not fall into the trap of shutting down the debate on difficult issues,” the source added.
“We have to call it out. If we fail to speak up for liberal values then we are simply yielding ground to reactionaries and extremists.”
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Mr Johnson’s remarks, in a Daily Telegraph article, have provoked criticism from Muslim groups, some Tory MPs and opposition parties.
In the article, Mr Johnson said full-face veils should not be banned but looked “ridiculous”.
The founder of the Conservative Muslim Forum said the remarks would harm community relations.
Speaking on BBC Radio 4’s The World at One, Lord Sheikh suggested Mr Johnson was “using Muslims as a springboard” for his ambition to lead the Tory Party.
“It is a joke but in very, very bad taste,” he said, adding that the former foreign secretary had a “weird sense of humour”.
Earlier, Foreign Office Minister Alistair Burt said there was a “degree of offence” in Mr Johnson’s comments.
On Twitter, Conservative Party chairman Brandon Lewis said he agreed with Mr Burt and called on the MP and former London mayor to apologise.
Former Conservative chairwoman Lady Warsi, the first Muslim women to sit in a British cabinet, welcomed Mr Lewis’s intervention and called for disciplinary action against Mr Johnson if he did not apologise.
She described the remarks as “offensive and deliberately provocative, but very clever politics”.
A debate about the burka should be had “in a serious way”, she said, rather than “trying to get airtime and attention on an issue which he knows will resonate with a certain part of the Tory Party”.
She added: “What offends me is that Muslim women are not a convenient political football to be used by old Etonians.”
Labour’s equalities spokeswoman Naz Shah said Mr Johnson should attend “training and engagement with the Muslim community” and called on Prime Minister Theresa May to respond.
“Clearly the Tory party has an issue with Islamophobia, but over 24 hours later the prime minister is still yet to say a word,” she added.
But Conservative backbench MP Andrew Bridgen said Mr Johnson had raised an important subject in a “light-hearted way”.
The reaction “says a lot about internal Conservative Party politics” he told the BBC.
Another Conservative MP, Nadine Dorries, said the government should apologise and that “Boris didn’t go far enough”.
What Boris Johnson said
In his Daily Telegraph column, Mr Johnson – who last month quit the government in protest at Prime Minister Theresa May’s Brexit policy – was commenting on the introduction of a burka ban in Denmark.
He said he felt “fully entitled” to expect women to remove face coverings when talking to him at his MP surgery – and schools and universities should be able to take the same approach if a student “turns up… looking like a bank robber”.
“If you tell me that the burka is oppressive, then I am with you,” he said.
“If you say that it is weird and bullying to expect women to cover their faces, then I totally agree – and I would add that I can find no scriptural authority for the practice in the Koran.
“I would go further and say that it is absolutely ridiculous that people should choose to go around looking like letter boxes.”
He said businesses and government agencies should be able to “enforce a dress code” that allowed them to see customers’ faces.
But he said: “Such restrictions are not quite the same as telling a free-born adult woman what she may or may not wear, in a public place, when she is simply minding her own business.”
He said a total ban on face-covering veils would give a boost to radicals who said there was a “clash of civilisations” between Islam and the West and could lead to “a general crackdown on any public symbols of religious affiliation”.