Defence Secretary Philip Hammond has admitted to raising the issue of sibling relationships in last week’s discussion about equal marriage with students at a university in Surrey – but says it was never about incest.

On Monday, a spokesman for the defence secretary said: “It’s untrue. He didn’t equate equal marriage to incest.”

Earlier, when asked by PinkNews.co.uk to clarify the remarks concerning incest and why it had been alleged that he had used the word in a conversation with students Joe Rayment and Jack Saffery-Rowe last Friday during a visit to the University of London Royal Holloway, Mr Hammond personally emailed PinkNews.co.uk: “The discussion ranged very widely and was not limited to same sex relationships.”

Later on Monday, Joe Rayment told the Daily Telegraph that Mr Hammond “definitely” made the comments attributed to him.

“We had a meeting with Philip Hammond,” Mr Rayment said. “During the meeting I asked him what right does the state have to tell two people who love each other that they can’t get married?

“He said, ‘Well we don’t allow siblings to get married either’.

On Thursday, Mr Hammond was forced to clarify his remarks during an interview on BBC Radio 5 Live Breakfast.

Presenter Phil Williams asked Mr Hammond on whether he had referenced about the state banning two siblings from marriage “Yes, I did,” the defence secretary told BBC Radio 5 Live.

“And the context was we were having a very wide-ranging discussion about the state and the state’s involvement in people’s relationships and people’s day to day lives, and also talking about the tax advantages that are available through marriage and civil partnership.”

Presenter Rachel Burden then asked the defence secretary: “Were you comparing homosexuality with incest?”

Mr Hammond replies: “No I was not – and that is a completely scurrilous interpretation of what I said.

Rachel Burden interrupts: “It’s not an interpretation, it’s a question.”

Mr Hammond replies: “And it’s one that I have already dealt with. I was actually talking about a situation that is familiar to many of my parliamentary colleagues, where elderly siblings are supporting each other, perhaps caring for each other – they are not able to access any of the tax advantages that married people or people in civil partnerships can access.”

When asked by presenter Phil Williams: “Can you see how answering that question with the sentence ‘we don’t allow siblings to get married either’ might be misinterpreted?

Mr Hammond replies: “I could see how someone who wanted to misinterpret it could misinterpret it”.

He then refers to the Guardian’s interview with Joe Rayment in which the student said the defence secretary did not mention the word ‘incest’ – however, Mr Rayment questioned the sincerity of his argument and told the paper: “We found this a very offensive and quite disgusting thing for him to say.”

Mr Hammond first went public about his opposition to equal marriage in May of last year when he said it was “too controversial”.

Earlier this month, he said: “I do not believe there is a compelling reason to prioritise legislation to go further at the present time and I have concerns about the robustness of the protections for religious organisations that are being put in place with the best of intentions.”