As a paid-up member of the Labour party, it’s rare that I agree wholeheartedly with a Conservative politician. But Boris Johnson has spoken some much-needed common sense in the gender debate. ‘When it comes to distinguishing between a man and a woman,’ the PM told MPs yesterday, ‘the basic facts of biology remain overwhelmingly important.’

Boris is right: biology does matter. I’d actually go further and say that the basic facts of biology are all that matters. Like other sexually dimorphic species we are male or female, and that alone distinguishes men from women.

We all know this but – in an astonishing departure from reality – these basic truths are denied by people who should know better, supposedly in an attempt to be kind to trans people like me. We are told that sex is no barrier to womanhood. This fallacy has taken root across politics, but it has flourished on the opposition benches. Only two weeks ago, Keir Starmer insisted that ‘a woman is a female adult, and in addition to that trans women are women.’

The trouble for Labour, however, is that it’s just not true. Women are female while transwomen are male. Female and male are different, so transwomen are not women. The logic is inescapable, but that has not stopped my own party’s MPs becoming lost in a muddle of their own making.

Johnson’s announcement came from the despatch box at PMQs in response to a question from Angela Richardson about the Cass Review into the children’s gender identity services at the Portman and Tavistock Clinic. Whether the question was planted or not, the PM knew exactly what he wanted to say. He immediately agreed to meet with Richardson – the Tory MP for Guildford – and then clarified ‘that when people want to make a transition in their lives, they should be treated with the maximum possible generosity and respect.’

Few people would disagree with that: the UK is a tolerant and welcoming society, and trans people enjoy the same opportunities as anyone else. Yet too many in the Labour party cannot see this. The party has been captured by gender identity ideology – an idealist philosophy that insists that feelings must take priority over material reality. In their cloud cuckoo land, if someone claims to be a woman then they are a woman. It is nonsense, of course, but it takes a brave Labour MP to stand against it.

While it is tempting to dismiss this debate as peripheral and irrelevant, the consequences of gender identity ideology are real. They matter. And it seems that Johnson realises that voters may also realise what is really going on here.

For a start, women’s rights are a lot harder to defend if we cannot even define the word woman. The impact on children – the context of Richardson’s question – has become even more profound. Young people have effectively been told they can choose whether to grow up to be men or women, without sufficient care about the impact on their mental health when that promise turned out to be hollow.

At the same time, trans people have also been let down dreadfully. While the Self-ID debate has become febrile, mental health support remains woefully inadequate. The prospect of changing a sex marker on a birth certificate in the back of a filing cabinet is small consolation for those trans people in need of help, but who are instead consigned to an interminable wait lists for specialist support.

Two years out from the next general election, the PM has taken a very clear position. Will Labour do the same? It is not good enough for Keir Starmer to babble on about it being ‘not right’ to claim that only women have a cervix. Voters on the doorstep are unlikely to be impressed by that nonsense, nor Angela Rayner’s dismissive claim that ‘Women’s rights are not in conflict with trans rights’. There is a conflict and it has ceased to be a niche issue on the margins of social media.

The Prime Minister has spotted an advantage and he has grabbed it. As he gave his biology lesson, he turned his eyes away from Richardson and looked at the party opposite. He knows – we all know – that unless Labour changes its position, their spokesmen and spokeswomen – assuming they know the difference – are going to look ridiculous every time they are posed a simple question: what is a woman?