Journalists and politicians talk a lot about freedom of speech, and rightly so, because the ability to express thoughts and opinions without fear or restraint is the foundation of democracy. We must be free to question, free to doubt, or we are not free at all.

But for journalists and politicians, 'freedom of speech' can feel a bit of an abstract concept, a debating point not a matter of personal safety. We talk about curbs on free speech as things that make it harder for us to do what we do – write and talk. We rarely think about them in terms of physical fear.

So a couple of weeks ago, when I wrote here about the way fear is chilling the debate about Britain’s laws on sex and gender, I really meant the fear of reputational damage. I referred to the fear that MPs and journalists feel that if they question moves to allow people to decide their own legally-recognised gender they will be accused of transphobia and bigotry.

That fear is real, and troubling, but there are worse things to be afraid of. Fear that you will lose your job and your livelihood. Fear of physical attack.

And that is what some people in this debate feel here. They fear that if they are seen to speak out and question the trend to change the law to allow 'self-identification', they will come to harm. Real harm.

Some of those people are meeting tonight in London, to discuss those changes in the law and their concern about them. I can’t tell you precisely where because the location of the meeting is being kept secret. The people organising and attending the meeting are scared of what might happen if some of the people who disagree with them turn up.

The people organising the meeting call themselves A Woman’s Place UK. They say the proposed changes in the law raise questions that are not just practical but existential. They worry that if a man can become a woman just by saying so, with no external check or verification, then the very term 'woman' becomes meaningless, and a group of people with no meaningful name or identity will in time lose all standing in law and society. For them, womanhood is a matter of objective biological fact, one that subjective feelings cannot change. Most, if not all, of them call themselves feminists.

Some of the people who disagree with them use a different name: TERFs. It technically stands for Trans Exclusionary Radical Feminist but if you follow online 'debate' you’ll see it’s become a term in its own right, and an abusive one. Follow the utterances of the most committed advocates of trans rights and you’ll find frequent references to violence against Terfs: punch Terfs, kill Terfs.

There are lesser threats too, to use more subtle means to inflict harm. Social pressure is used to threaten the employment of those considered Terfs: read this Mumsnet thread for a disturbing litany of what happens to women who ask questions about the self-identity agenda in the workplace, especially in academia and the public sector. In politics, women who question the self-ID agenda have faced censure and expulsion in Labour, the Greens and, yes, the Women’s Equality Party.

It is hard not to conclude that such things are at least partly the result of a concerted attempt to stigmatise and demonise women who attempt to raise concerns about a policy that they feel poses risks to their safety and even their fundamental existence.

To be clear at that point, I note that the following two statements can both be true, at the same time. Neither fact justifies the other. First, some transgender people suffer unacceptable physical, mental and social abuse that causes them real and unacceptable harm. Second, some women who question the move towards self-defined gender feel real and unacceptable fear of physical harm at the hands of some people who advocate that change in the law.

Perhaps you think a Woman’s Place UK are over-reacting, or talking up the threat for political purposes. If so, I suggest you search online for 'punch terfs'. Or follow a case of alleged assault currently awaiting trial. Or review the history of the group’s Edinburgh meeting, where one of the protesting groups has demanded that the venue that had the temerity to host a bunch of women talking about feminist theory hand the proceeds of the event over to a group that says punching Terfs is a moral duty akin to fighting Nazis.

Against which background, I suggest that it is depressingly understandable that some of the women involved in tonight’s meeting feel genuinely threatened, and threatened over the simple act of attending a political meeting.

And for all that this might upset or even offend some people, biology does matter here. Biological males are, on average, larger and stronger and more aggressive than biological females. Biological males commit more acts of violence -- and more serious acts of violence – than biological females.

For these sadly rational reasons, among others, women are more likely to feel afraid of men than men are of women. Hence the existence of those spaces and places that law and convention reserve for women: changing rooms, refuges, hospital and prison wards.

Would the safety of those spaces be compromised if any man could gain the legal right to enter them simply by saying the words 'I am a woman'? That is one of the questions the women who meet tonight are asking -- keenly aware that some of the people who might take up that legal right are currently issuing threats against them.

I don’t know the answer but I think the question is a valid one and deserves a considered answer from anyone who proposes to change the law to allow such a situation. But it appears that some of those people don’t want to answer the question. They don’t even want it to be asked.

So the story of tonight’s Women’s Place meeting is this: a group of people who were raised male and in some cases retain full male anatomy are perpetuating a narrative that harm – including physical violence -- can and should be inflicted on women who question the things those people say are true.

This debate about gender and sex and identity may seem terribly modern, a product of our times, but really, this is a story as old as they come: women who do not know their place are threatened and punished. Britain in 2018 is still a country where women who speak out risk a smack in the mouth.