Rowan Atkinson has defended Johnson for his comments, for which he has since apologised.
The party has received complaints that the comments breach its code of conduct, and under Conservative rules they must be investigated by an in- dependent panel.
He wrote: "As a lifelong beneficiary of the freedom to make jokes about religion, I do think that Boris Johnson's joke about wearers of the burka resembling letterboxes is a pretty good one". 'Completely entitled to say it'Jacob Rees-Mogg, Tory MP for North East Somerset " He's completely entitled to say it and there's nothing to apologise for", Mr Rees-Mogg told Nigel Farage on LBC.
But Mrs May, amid calls from Tory peer Lord Sheikh for Mr Johnson to be removed from the party, has insisted Mr Johnson apologise, saying his remarks "clearly caused offence".
"You should really only apologise for a bad joke".
"The burqa and niqab are disgusting tribal ninja-like garments that are pre-Islamic, non-Koranic and therefore un-Muslim", he wrote in The Times.
One backbencher told The Independent the handling of the affair by Ms May and other party leaders had been so poor that it has increased the chances of a leadership challenge over the summer.
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"We are not bound by collective responsibility or that type of discipline and it is the wrong approach to party discipline".
Critics claim Johnson is using the burqa comments to boost his appeal among right-wing members of the party.
Mr Mitchell retorted: "We must keep some perspective; I don't agree with what Boris said - I think women should be allowed to wear what they want - but I do think we must careful not to go over the top on this".
Joining Julia Hartley-Brewer on talkRADIO, he said: "I think a lot of your listeners will be deeply anxious about the state of our democracy and free speech".
He added: "But let's look at what Boris said: he expressed himself in quite colourful language".
A hundred Muslim women who wear the niqab or burka have signed a letter to Lewis, calling on him to withdraw the Conservative whip from Johnson and launch an independent inquiry into Islamophobia in the party.
"I think it's a very dark day for our democracy and free speech and I'm deeply anxious that this policy is being adopted by the Conservative Party, if we're not the party of free speech, then who is?" "Nevertheless we do so because we believe it is a means to get closer to God", the women said in a letter.