Boris Johnson is defying calls from Conservative party chiefs to apologise for his claim that Muslim women in burqas resemble letter boxes and bank robbers.
The former foreign secretary is understood to view the instruction as an attempt to shut down debate on a difficult issue that should be tackled head-on.
But his refusal to say sorry directly defies an order from the Tory chairman, Brandon Lewis, to do so, and increases pressure on Theresa May to intervene.
One source close to 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.
“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.”
Earlier, Lewis said he had asked Johnson to apologise for his controversial remarks in an attempt to draw a line under the Islamophobia row.
It came after Alistair Burt, the minister for the Middle East, who worked under Johnson, described the comments as offensive and said he would never have said anything similar.