I was visiting some friends the other day and got talking to their 14-year-old daughter about a film she’d just watched: The Iron Lady, Meryl Streep’s movie about Margaret Thatcher. So what did you think of it, I asked. “Mrs Thatcher was awful,” she said.

OK … because I was actually there, I was able to mansplain the subject to the teenager and I think I could detect, in the moments she glanced up from her phone, that she was deeply impressed by my arguments. We talked about the Falklands, and Scottish jobs, but we also talked about gay rights. My friend’s daughter knew all about Section 28.

The specific question we discussed was whether the Tories have a good record on LGBT issues, and the fact that teenagers do know about Section 28 is interesting. The infamous law sought to ban the promotion of homosexuality in schools and yet it’s now at the heart of lessons about the persecution of gay people. I like the irony of that: Section 28 is changing education but not in the way intended.

The weird thing about that notorious law however, is it’s really an aberration in the Tories’ legacy. What my friend’s daughter apparently hadn’t been taught in school was that homosexuality was decriminalised in Scotland in 1980 – under Margaret Thatcher of course – or that it was the Tories that introduced gay marriage. The Conservatives are also the gayest party by far, with a large number of out MPs and MSPs, and in the last few days they’ve also become the first party to have an openly transgender MP.

So what’s going on? And why would so many gay people like a party that’s supposed to not like them? There’s not an easy answer to that question, but it’s always been there (Mrs Thatcher herself had a good number of gay men in senior jobs). Perhaps it’s because sexuality doesn’t actually define our political beliefs, or perhaps it’s internalised homophobia, or perhaps it’s because the record of the Conservatives on LGBT issues is actually rather good on the whole.

Except that now we have the problem of Boris Johnson and conversion therapy. In some ways, Johnson is typical of modern Conservatives in that, socially, he’s extremely liberal but on conversion therapy he’s in a fankle. He promised a ban then he changed his mind then he changed his mind again so now the ban on conversion therapy will only cover the LGB bit and not the T. It’s led to the resignation of one of the government’s advisors.

Perhaps the problem in the end isn’t the Tory party, it’s – quelle surprise – the party leader. During the AIDS crisis, Mrs Thatcher (who was a scientist remember) was interested in the facts and based her policy on those facts – she was thorough in other words and Boris Johnson is anything but. He’s a skimmer and rarely appears to have a deep understanding of the subjects on which he’s legislating.

Let me tell him then. I’ve spoken to people who’ve undergone conversion therapy; one young man told me he felt suicidal and had nightmares. But he also told me that what the government needs to do is simple: ban anything that’s based on the belief that a person’s sexual identity or gender identity can and should be changed. Surely that’s simple enough, even for the PM.

If he still doesn’t get it, the consequences for the Conservatives are bad. It also doesn’t help that the Scottish Tories are all over the place on the issue. They say they will diverge from the UK Government and support a ban on conversion therapy including for trans people, but they also say they do not support the Scottish Government’s gender recognition reforms. Have they thought this through?

It also leaves voters like me, and voters-to-be like my friends’ 14-year-old daughter, uncertain about whether the Tories can be trusted on LGBT issues. As I say, their record is actually quite impressive and a good number of gay people like what the party says on other issues. But if you’re going to be seen as a gay-friendly party, you’ve got to prove it. And it’s a test Boris Johnson is starting to fail.

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