It may sound a little melodramatic to say that human rights are under attack in Britain. But in the week I opened this book, it certainly didn’t feel that way. Parliament was locked in battle over the Rwanda bill, widely seen as driving a coach and horses through human rights obligations, with Shami Chakrabarti herself in the thick of the fray as a Labour peer. Nigel Farage was once again demanding Britain leave the European convention on human rights – the new passion project for Brexiters who would rather not talk about how Brexit itself is going, and who see the convention as a haven of suspiciously lefty values – while Rishi Sunak was bending over backwards not to rule that out. There’s still something faintly surreal about having to actively make a case for the right to life, liberty, or freedom from being tortured – who doesn’t automatically value these things? – but if Brexit taught us anything, it’s that liberals are surprisingly bad at defending truths that seem so obvious we’ve never given them much thought. This time, it pays to be ready.

Chakrabarti has already covered some of this ground in her brilliant first book, On Liberty, in which she reflected on her time running the civil liberties organisation of that name and somehow pulled off the rare feat of tackling extremely serious issues without taking herself too seriously. This third book, however, feels more like sitting through an undergraduate lecture, albeit an absorbing one.

It begins with a useful primer for the layperson, explaining the basic rights and principles underlying the sort of morally complex arguments – over free speech on university campuses, or whether the famously strict Michaela school can ban pupils from praying, or whether Israel has committed war crimes in Gaza, or whether a Christian baker can be fairly expected to bake someone a wedding cake for a same-sex couple – that keep hitting the headlines.

For Chakrabarti, however, the ECHR isn’t just a set of amalgamated legal safeguards but a source of “sheer poetic insight” into human nature: she sees a lyricism in the language and something moving in the way it flows from the rights of the individual to rights governing the way we interact as social animals, form families, speak to one another, or keep secrets. This is law essentially willing civilisation into action, and as with difficult music or the higher reaches of maths, there is a hidden beauty in it. What she describes is an extraordinarily delicate balancing act in which war can sometimes trump the right to life, and yet must still have its strictly ordained limits. (The right to be free from torture, for example, is still absolute even when soldiers are killing one another on the battlefield; or it is, at least, in theory). By the time the author announces her intention to defend this feat of moral engineering from “some extremely common and trenchant criticisms”, I was practically ready to man the barricades for poor misunderstood activist lawyers. And yet somehow, that moment never quite came.

Chakrabarti systematically picks apart a number of critiques – some technical, and some now decidedly niche, including an anti-capitalist attack on human rights law (for protecting the property interests of the super-rich and being employed against abuses in China or Russia) that reads remarkably like the radical left eating itself. She does touch on some fascinating arguments, though, about how to enforce human rights principles online, or how they might help guide a just transition to net zero.

But she circles only in surprisingly wide loops round the most common and most serious attack now made against the ECHR, that by getting in the way of things many Conservatives want to do – often to immigrants, or protesters – the law has made itself an enemy of the people, stopping democratically elected politicians doing what the public wants. Something similar happens in the chapter on what happens when rights clash, which reads at points as if it’s about to engage with the argument over transgender rights and women’s rights but never quite does.

Chakrabarti clearly didn’t want this to be a political book, to the point of apologising if any reader has found her too political. Though unusual for a former shadow cabinet minister, that’s nonetheless understandable: the whole point of human rights law is that it’s meant to be above such things. But since the nature of the attack is now intensely political, failing to confront it directly leaves the rebuttal feeling rather incomplete. The defence cannot, in the end, rest here.

• Human Rights: The Case for the Defence by Shami Chakrabarti is published by Allen Lane (£20). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply