David Cameron’s support for equal marriage amid widespread opposition from many of his Conservative MPs remains an apparent mystery to his mother.

According to the Telegraph, at a recent lunch, Mary Cameron was asked why her son was pressing ahead with legislation when it was supposedly ‘alienating’ Conservative supporters.

“I know, but David just won’t be told,” she replied.

Mrs Cameron, 78, whose father was Sir William Mount, 2nd Baronet, is a retired Justice of the Peace.

The government published its Marriage (Same Sex Couples) Bill for England and Wales on Friday.

It has divided Conservatives, with former Defence Secretary Liam Fox recently describing it as “ill thought through and constitutionally wrong”.

However, the bill is likely to secure a majority in the Commons with the support of Labour and Liberal Democrat members.

The second reading will come on 5 February, and then the bill will have to pass through committee and report stages in the House of Commons, as well as a third reading.

It will then have to go through a similar process in the House of Lords.

In 2011, the prime minister told the Conservative Party Conference: “to anyone who has reservations, I say this: Yes, it’s about equality [equal marriage], but it’s also about something else: commitment. Conservatives believe in the ties that bind us; that society is stronger when we make vows to each other and support each other.

“So I don’t support gay marriage in spite of being a Conservative. I support gay marriage because I am a Conservative.”