“As a liberal, I’m passionate about equality, and equal marriage, about equal rights for LGBT people, for fighting not just for LGBT rights in this country, but overseas.”

That’s Tim Farron, leader of the Liberal Democrats. He’s a man who voted for the same-sex marriage bill on its second reading in 2013 (he was absent for its third reading – something he has said he regrets), and voted to make those rights available to members of the armed forces in 2014.

And yet, we keep asking him to tell us exactly what he thinks about gay sex. Why?

He’s a committed Christian. One of those evangelicals, who believes in the inerrancy of the Bible? He doesn’t like labels. Instead, he says: “My faith is in Jesus Christ, I put my trust in Him. I count Him as my Lord and saviour, and I’m in no way ashamed of that.” What’s clear is that religion isn’t simply a part of his identity, an inheritance, as it is with vicar’s daughter Theresa May. It’s front and centre, an active choice: he was baptised when he was 21.

I suspect that means he does in fact hew pretty closely to what the Bible says. I wouldn’t be surprised if he takes the passage in Leviticus 18:22 – “Do not lie with a man as one lies with a woman. It is a sinful thing” – at face value.

How else to explain his answer, when repeatedly pressed on the issue by Channel 4 anchor Cathy Newman in 2015? “We are all sinners ... the Bible phrase I use most is ‘you don’t pick out the speck of sawdust in your brother’s eye when there is a plank in your own’.” In that formulation both sawdust and plank are sins – it’s just not a Christian’s business to go around dressing people down for their faults.

When Newman asked him the same question on Tuesday, he sidestepped it once more. “I’m not in a position to go making theological pronouncements.” His job is to lead a party with a platform squarely behind gay rights. In that context, he seemed to be saying, what he thinks God thinks about sodomy is irrelevant.

That makes lots of people uncomfortable. The Liberal Democrats are the original party of the easy-going metropolitan elite. If you discount the homophobic campaign against Peter Tatchell in 1983, they’ve usually been way ahead of the curve when it comes to LGBT rights. The leader of their predecessor party, Jeremy Thorpe, had relationships with both men and women.

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But I’m inclined to agree with Farron. The advancement of LGBT rights doesn’t depend on us all celebrating gay sex with every fibre of our being. It depends on a consensus in which the rights of minorities are protected – and really flourishes under secularism: a framework where religion is not obliterated, but accommodated without special privileges alongside other beliefs.

I don’t need a window into Tim Farron’s soul. I don’t care what he considers sinful, so long as it doesn’t translate into policy. For that reason, however, he should be watched like a hawk for any hint of discriminatory lawmaking. In 2007, he voted against banning discrimination in the provision of services to people on the basis of their orientation (Theresa May didn’t vote, Jeremy Corbyn voted for). But if the quote at the top of this piece is anything to go by, he’s been on a journey – like many in a House of Commons that only managed to repeal the homophobic section 28 in 2003.

In any case, he knows he’s toast if he starts threading the Lib Dem manifesto through with Old Testament edicts. Homophobia is rightly deemed a serious political transgression these days. But can we extend to Farron the same courtesy he affords us, and love the sinner, while hating the sin?