Boris Johnson is facing an investigation into breaches of the Conservative Party code of conduct.
The party has received dozens of complaints about the ex-Foreign Secretary’s comments about Muslim women wearing burqas.
The complaints will be looked at by an independent panel which could refer Mr Johnson to the party’s board, which has the power to expel him.
The party declined to comment on the details of the investigation.
A Conservative Party spokesman said: “The code of conduct process is strictly confidential.” A source close to Mr Johnson offered no comment.
Mr Johnson has rejected calls to apologise for saying people wearing burqas looked like “letter boxes” or “bank robbers”, in a Daily Telegraph column in which he also argued against a ban on full-face veils.
Critics have accused him of stoking Islamophobia to boost his Tory leadership ambitions but his supporters have said he was speaking up for “liberal values”.
Meanwhile, according to a survey by Sky News, six out of ten people said it was not racist to compare Muslim women wearing the Islamic face veils to “bank robbers” and “letter boxes”, while just 33% thought it was.
The poll was conducted after former Foreign Secretary Boris Johnson made the comparisons in an article for The Telegraph newspaper.
The poll also revealed that Britons remain split as to whether Johnson should apologise for his remarks – 45% think he should do so, while the majority, 48%, think he should not.
People from the capital city London were the heaviest critics of Johnson, a man they twice elected London mayor, with over 50% saying he should apologise for the Islamophobic remarks.