The plight of homeless people, and our reaction to it, are part of the hideous tangle this country has got into. There are so many strands leading into this appalling knot, that if we pull any one of them, the tangle gets worse.

So the question of why decent men and women find themselves able to walk past people begging in the street, or huddled up in doorways with only layers of cardboard to keep out the cold, is all mixed up with the flagrant deficiencies of Britain’s democracy, and the craven desire to suck up to the US that brought us the “war on drugs” among other idiocies, and the extraordinary grip that the public schools seem to have on the levers of power.

And then there are the facts that the ice caps are melting, and our utilities are now in the hands of foreign corporations, and that teachers are treated with hostility and suspicion, and that Russia interferes with our politics, and that libraries are closing, and the transport system is an uncoordinated mess, and people are dying on trolleys in hospital corridors, and that senior politicians see fit to deny that the government has anything to do with people being poor, and claim that the victims of Grenfell Tower died because they had no common sense. And universal credit. And the gig economy. And zero-hour contracts. And the flagrantly biased media. And Brexit. And on and on and on. All part of the same thing. Why do we tolerate it? Any of it.

Lies, cowardice and betrayal leak from the very pores of our political leaders; trust limps after them like the poor little dog following the murderer Bill Sikes in Oliver Twist

We’ve become complacent about moral progress. We look at the great advances in science and medicine and sanitation in the past couple of centuries, and we congratulate ourselves that improvements in those fields have been accompanied by advances in moral understanding. These days we don’t gather to watch bears being tormented to death by dogs, or heretics having their intestines pulled out while they are still alive. We believe that Britain is a kindlier, more decent place than it used to be.

I think it may have been, once, for a generation or so, beginning with the Clement Attlee government and the creation of the National Health Service. The idea that there was such a thing as a postwar consensus has been defended by some historians and criticised by others, but I remember it: it is embodied for me in the memory of Battersea park, where I wandered as a boy and looked at sculptures by Henry Moore, and at the Pleasure Gardens created during the Festival of Britain, and where the park keepers might have told us off for climbing the trees but we somehow knew they were part of what kept the place safe and orderly.

There was a common understanding of the value of civic decency. There really was such a thing, and many of us really believed in it. My parents and grandparents did; my teachers did.

And then it began to vanish, almost invisibly at first. Little by little, an acid rain began to dissolve the structures of thought and feeling that gave us healthcare and libraries and schools and council houses and public parks. By the 1980s, it was working its way deep into our politics and our lives. The public life of this nation has decayed into a state of moral squalor. Lies, cowardice and betrayal leak from the very pores of our political leaders; trust limps after them like the poor little dog following the murderer Bill Sikes in Oliver Twist, even though Sikes is going to kill him.

Nothing can grow in this poisoned wilderness except money. Shame, which needs the soil of conscience before it can take root, can’t flourish here; little shoots tentatively appear, only to fade and droop and die in the corrupted air. Imagine Boris Johnson expressing shame. Imagine Donald Trump doing so. Why feel shame? Who needs shame? Shame is for losers.

Facebook Twitter Pinterest Boris Johnson reaches out to shake hands with Donald Trump before a Nato leaders’ meeting in Watford, December 2019. Photograph: Francisco Seco/AP

In the doorways of great, stony-hearted buildings, in urine-stinking underpasses, under crumbling bridges, people who have nowhere else to go lie down to sleep. And we go past – I go past – and perhaps drop a few coins on a blanket or in a cardboard box, and then go home to our comfortable houses and watch the TV news, where we learn with a sinking heart about the latest opinion polls.

What can we do? Where do we start? Which thread in this abominable tangle of misery and stupidity and greed and wickedness should we try to pull first? And what hope could we have that it would start to untangle the rest?

The classical response to a Gordian knot like this would be to slash it through with a sword; and yes, that would work, briefly. Violent revolution as an expression of rage and despair does change the state of things for a while. The trouble is that it swiftly makes everything even worse. The only person to benefit from cutting the Gordian knot is the one with the sword.

So what do we do? Sink into a torpid and surly despair? Rise above it in a mindful bubble of self-enclosed bliss? What on earth can we do?

Election polls UK 2019: Tories maintain lead over Labour as campaign enters final days Read more

This question came home to me powerfully when I read the Guardian’s series about the deaths of homeless people, because I realised that I had taught one of them. Sharron Maasz was 44 when she died, having suffered domestic abuse and mental health problems as well as drug and alcohol addiction. I taught for a while at the school she attended in Oxford, but to be honest I can’t really remember her, no doubt because she was friendly and well behaved. And the city where I live, the society I’m part of, could do nothing to keep her alive.

We need individual acts of charity – of course. But they’re just drops of water when what we need is a flood. We need political change – by all means. Let’s have a system that liberates us instead of choking the possibility of a decent life for everyone. But I’m coming more and more to believe there’s something in us that relishes wickedness and nourishes stupidity, something much deeper than political systems or economic theory.

For much of my lifetime, that something was kept in check by other equally ancient human impulses: kindness, empathy, cooperation.

But the balance has swung the other way – perhaps not by much; perhaps by 52% to 48%, for example. It’s time to help it swing back again. We have to develop, or perhaps evolve, a moral understanding that is wider and more clear-sighted than the one displayed by our current leaders.

And we have to do it soon, and we can only start from where we are. On Thursday, we have a general election. As usual, if we live in a constituency that’s a safe seat, our vote will count for nothing. But those of us whose constituencies are marginal must – must – vote tactically and stop the current administration in its tracks. That would be a start, and then the real work could begin.

• Philip Pullman’s latest book is The Secret Commonwealth: The Book of Dust Volume Two