LAST Thursday’s assassination of Labour MP Jo Cox in her Batley and Spen constituency is a tragic reminder of how quickly the politics of fear can turn into the politics of hate.

The outpouring of grief up and down the country over the senseless loss of this talented and popular parliamentarian has a single question at its core — why?

There are no easy answers. Severe mental illness, neonazi radicalisation, a poisonous political climate — all of these may be factors, but they don’t explain why someone would shoot and stab a well-loved local MP before kicking her blood-soaked body.

Only one thing can explain that — hate. But where did it come from? And where does it go from here?

We saw the same hate so recently at the Orlando gay nightclub massacre. It was there at the Paris police officer’s execution, broadcast live online.

And it was in Marseille when English, Russian and French football fans rained tribal violence on each other in the face of tear gas and water cannon.

But we can also see it at Trump rallies, where the frenzy and passion inspired by racist promises to ban Muslims and build walls can reach almost shamanic proportions.

And we can see it while walking down the street here, with Nigel Farage’s nazi-esqe new poster screaming down at us that Britain’s at “BREAKING POINT.”

Perhaps we really are at breaking point. Not in a far-right racist way — there’s plenty of space and wealth in Britain to share with whoever makes it to our shores — but it’s beginning to feel like we’ve reached our limit psychologically.

Maybe it’s the months of “project fear” we’ve endured from both sides of the EU debate, or possibly the years of painful austerity and the shredding of our social contract, but people have had enough.

We’ve had enough of scary statistics claiming we’re one bad choice away from economic armageddon.

We’ve had enough of being divided and turned against each other — whether it’s Inners versus Outers or workers versus shirkers.

We’ve had enough of seeing internal tensions within our communities exploited for political advantage, leading to record levels of Islamophobia and resentment towards immigrants.

We’ve had enough of a Tory civil war in which both sides seem willing to sacrifice any principle for the sake of power, no matter the damage to our economy or political process.

And we’ve had enough of the unedifying Labour infighting — from anti-semitic smears to very public coup plots. Whether it’s MPs calling Ken Livingstone a “disgusting nazi apologist” or Corbynistas hissing at a BBC journalist, we seem to have woken up in a nastier world of toxic politics.

Social media shares some of the blame — and when troll culture climbs off the web into “real life” it’s bound to bring new dangers with it.

Cox’s death affects us all so deeply because she was an MP representing over 100,000 constituents who was gunned down in the line of duty. Symbolically, this was a mass murder.

Over the next few days, we’ll find out much more about suspected killer Thomas Mair. Right now, it’s being reported that he had links to South African white supremacists, as well as US neonazis from whom he’s said to have bought weapon-making manuals.

When asked his name in court on Saturday, Mair replied: “Death to traitors, freedom for Britain.”

The attacker is reported to have shouted “Britain First” while carrying out his terrorist act, though it’s unclear exactly what was meant by this.

BNP splinter group Britain First has denied any connection, with its leader calling for the perpetrator to be “strung up by the neck from the nearest lamp-post — that’s the way we view justice.”

It’s natural to want revenge. But we’d all be better off if we followed advice to hate things, not people — and that means resisting the temptation to view Mair as evil incarnate.

Because the truth is, if we don’t try to understand why he apparently did something so awful, or why Omar Mateen killed all those people in Orlando, or why football fans enjoy smashing chairs over each other’s heads, we won’t get anywhere.

Hatred breeds hatred. If we continue to caricature or demonise people we consider different to us, we can’t be surprised when they respond in the same manner.

Whatever way we self-define, we always risk cutting ourselves off from common humanity.

Nowhere is this more apparent than in our appalling treatment of refugees. Throughout her 13 months as an MP, Cox spoke up passionately for asylum-seekers, playing a high-profile role in forcing the government to offer 3,000 Syrian children sanctuary.

She also spent much of her working life in the world’s most dangerous places helping the most vulnerable people. It’s hard to think of someone less deserving of this murderous hate.

Cox was clearly a born campaigner and independent spirit. Her London residence was a houseboat on the Thames from which she sometimes commuted by dinghy to the Commons.

The day before her death, Cox earned Out ire for confronting Farage’s flotilla on the river, holding aloft an In flag with her husband Brendan and their two children.

Brendan later tweeted a picture of someone on a Vote Leave boat hosing them all down with water.

Her murder is a warning that the far right is rising, that intolerance and bigotry are the new norm for many and that the forces of reaction aren’t giving up without a fight.

It’s up to all of us now to take some time out and reflect on our own lives and beliefs. Everyone has flaws and suffers from prejudice, but irrational hatred is our most dangerous emotion.

Now more than ever we need to reach out across the social and political divide and try to understand how other people think and feel.

Whether or not the referendum was a factor in this terrible crime, it’s clear that, by calling it, David Cameron unleashed a tsunami of chauvinism he never had a chance of controlling.

Others have played their part in polluting the political environment, but as prime minister the buck stops with him.

Someone needs to unite a frightened and confused country against the nightmare of ultra-nationalism and lead us through the grim days and weeks ahead.

If Cameron somehow survives his reckless referendum, this will surely be the most important challenge he’s ever had to face.

• Chat to Charley on Twitter: @charleyallan