Conservative MP Sir Peter Bottomley has given a robust defence of David Cameron’s support for same-sex marriage and says the media’s interest in sex has overblown the debate.

The West Sussex Tory MP for Worthing West played down opposition from local Conservative officers who have petitioned Downing Street over the issue.

On Sunday, around 20 former and serving Conservative chairmen were seen handing a letter into Number 10.

Speaking on BBC Radio 4’s Today programme, ahead of Tuesday’s vote on the Marriage (Same Sex Couples Bill) by MPs, Sir Peter accused the media of overstating the significance of the petition.

“There are, say, 630 associations, there’s now two active officers for each one, that’s over 1200. Twenty five past and present officers went to Downing Street – 25 out of over 1,000, 2,000, 3,000 – doesn’t strike me as newsworthy.”

Sir Peter continued: “Conservatives believe in fairness, we now understand that to move from a civil partnership to civil marriage is to allow the words ‘I will’ at the ceremony, with the registrar. It’s not going to be a big deal. So I think somehow, whether it’s Conservative MPs, whether it’s campaigners, whether it’s some of the media, they’ve said ‘Oh, there’s sex in this, let’s give it more prominence than it deserves’.

Sir Peter pointed out how far the debate on gay rights has come since he first became an MP in 1975.

“We don’t know how they’re going to vote yet because we haven’t had the vote, let’s have the vote tomorrow and then count. Then let’s look back to when I came into parliament in the 1970s after Margaret Thatcher had been one of the Tory MPs who, as a minority, had voted to decriminalise homosexuality, most people forget that.

“In 1975 when I was elected, others were being selected, you had to say you were in favour of capital punishment to get selected. I’m not accusing any of my colleagues of twisting their views but I think if anyone said ‘are there similarities?’, I’d say, ‘ask them’.”

He denied that most people were against equal marriage and predicted opposition would diminish over time.

“No, all the evidence shows that 60-40 people are content with this, I don’t think the majority is [opposed], but those who are over-65 tend to be 60-40 against. People up to 65 tend to be 60-40 or more in favour. It’s generational, it’s not age it’s generational.

“We’ve seen massive change. All we’re really saying is ‘should sexuality be a bar to making a lifelong commitment to another person?’. Civil partnerships were opposed by 40% of people when they came in five years ago, they’re now opposed by about 8% – so three-quarters of the opposition vanished when people experienced it in others.”