"When we receive a formal complaint, we will investigate it in a timely and confidential manner".
Schools and universities should be able to take the same approach if a student "turns up. looking like a bank robber".
Mr Johnson will be given the opportunity to make a statement providing "any evidence or details that will help to establish their position".
"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".
Johnson labelled Muslim dress "oppressive", and claimed of the niqab: "It is absolutely ridiculous that people should choose to go around looking like letter boxes".
"Is Islamophobia, in fact a "natural reaction" or is it one of the by-products of a white, male-dominated Government, which continues to spew racist and sexist rhetoric, diminishing the status of Muslim women as British people?"
Former attorney general Dominic Grieve - a long-time opponent of Johnson - even suggested he would leave the Tories if Johnson were elected leader, saying "I don't regard him as a fit and proper person to lead a political party".
Matthew Seiyefa Confirmed as New Acting DG DSS, Meets Osinbajo
On Tuesday, masked security operatives were seen blocking access to the parliament building in the capital Abuja. It is not clear if the meeting scheduled for Tuesday afternoon will still hold after today's turn of events.
What led to his remarks?
Johnson's comments were condemned by members of the opposition Labour Party, while the Muslim Council of Britain (MCB) reiterated its call for an inquiry into allegations of Islamophobia within the ruling Conservative Party.
Meanwhile other MPs have leapt to his defence.
The letter, seen exclusively by Sky News, says an apology would be "insufficient" and that Mr Johnson made a "deliberate choice" to "inflame tensions in a way that makes it easier for bigots to justify hate crime against us".
In the first instance, Johnson - a leading figure of in the campaign to Leave the European Union - will be scrutinised by a party investigator.
The independent panel will decide whether to refer Mr Johnson to the party's board.
The repercussions could exasperate the party's growing civil war, where the debate over Johnson's comments has developed into a proxy war between Brexiteers and Remainers in the parliamentary party.