A person can defend the same principles for forty years and find themselves described as a conservative by people who once would have called them a radical. If what they are defending is free speech, equal treatment and secular law, I think we should be asking why the label changed.
The fight for those freedoms was real. People challenged institutions with the power to punish them for what they said, who they loved or the place society had assigned them. Many of their demands became ordinary expectations of British life. The victories were never complete, but enough changed that defending those gains is now part of the job.
Wanting to keep them doesn't mean abandoning liberalism. It may mean taking it seriously.
The case for going further
Critics have a reasonable objection. Equal rules don't remove every inherited advantage. People can have the same rights in law while facing very different circumstances. Free expression can also be easier to bear when you have the money, confidence or influence to answer back.
Those are real problems. Saying "the rules are equal" doesn't make them disappear. The disagreement concerns what we should do about them.
I worry about remedies that make a person's rights depend on the group they belong to, or allow authorities to suppress ideas because they judge them harmful. Who gets to make those decisions? What happens when they are wrong? What can someone do when the authority meant to protect them is the source of the unfairness?
We need to be able to challenge power under rules that apply to everyone. Once equal treatment and open argument become things that can be withdrawn from the wrong person, the protection is much less reliable.
The freedoms we expect people to respect
Britain contains people with very different beliefs. Some oppose equality for women, the freedom to leave a religion or the right to criticise it. We should be able to say that plainly. We should also recognise that people from every background defend those freedoms, often against considerable pressure within their own communities.
The relevant distinction is what a person believes and does. Refusing to criticise an illiberal belief because of who holds it helps nobody who has to live under it.
What Popper's argument actually allows
Karl Popper's paradox of tolerance is often invoked to justify shutting an argument down. His discussion in The Open Society and Its Enemies, volume one, chapter seven, note four, is more qualified than that.
He argues that unlimited tolerance can allow intolerant movements to destroy a tolerant society. But he also says that suppressing their views would be unwise while rational argument and public opinion can counter them. His concern includes movements that reject argument and encourage their followers to answer it with violence.
That is a serious warning about defending an open society. It isn't a general permission to censor anyone whose opinions we find offensive.
The liberal settlement needs improving. It also needs defending. Equal treatment and the freedom to challenge an authority are among the ways people can improve it. I don't think giving those up would make us more progressive, whatever we chose to call ourselves afterwards.