SOCIAL media is full of amusing videos: cats meowing like opera singers, squirrels doing high wire somersaults. But sometimes you come across a gem that opens your eyes very wide indeed.

Recently I discovered just such a clip. It was a report by journalist Peter Oborne on the effect of a no-deal Brexit on Northern Ireland. (Simply Google: Peter Oborne Belfast Telegraph if you want to see it).

Oborne’s sobering report made me realise just how much we have to lose if the “Get Brexit over with on 31st October whatever the price” position, championed by our own Prime Minister, becomes reality.

Perhaps the most moving interview was with an old man. Alan Black was the sole survivor of the terrible Kingsmill Massacre, a mass shooting that took place on 5 January 1976 near the village of Whitecross in County Armagh, Northern Ireland. IRA gunmen stopped a minibus carrying eleven workmen, lined them up alongside the vehicle and gunned them down. Only one victim survived, Alan Black, despite being shot 18 times.

Mr Black commented: “To go back to them days is unthinkable”. He described the peace brought about by cross-border accords in the Good Friday Agreement as “not perfect . . . but it is a peace“. Movingly, he added, “My grandkids can grow up without worrying about bomb or bullet.”

It is easy to forget the levels of fear, violence and hatred between and within communities in Northern Ireland at the height of the Troubles. Atrocities and senseless killings were committed by all sides, as you would expect in any war, whether it is fought by conventional armies or terrorist gangs. The point, as Winston Churchill pointed out, is that always “Meeting jaw to jaw is better than war.”

Which is why the current Brexit crisis is so alarming when it comes to Northern Ireland.

Nor is the general context encouraging. The collapse in December 2017 of power-sharing arrangements between the DUP and Sinn Fein seems no nearer resolution. Such a situation is dangerous enough in itself, threatening the very nature of the Good Friday compromise.

The possibility of a hard border returning between Northern Ireland and Eire by casually bulldozing through a no-deal exit from the EU could be just the excuse potential terrorists have been waiting for.

So far Boris Johnson has talked often about “technical solutions” to the fact that tariffs will work both ways for cross-border trade when we leave the EU. Yet none of them have been adequately explained.

Indeed, last week Leo Varadkar, the Irish Taoiseach, said tariffs would apply to "goods imported into Ireland from the United Kingdom and vice versa" in the event of a no-deal Brexit. "The tariff schedules are already known . . . You will need to be registered as an importer-exporter and you will need to make customs declarations."

Let us not fool ourselves. The only way such a system could work is through re-establishing border checkpoints. And so, slowly, and no doubt reluctantly, the clock of history would be turned back in Ireland.

Let us never dare to forget how complex – and often bloody – the relationship between Ireland and the UK has been for centuries. Many people reading this article will remember bombs going off in major English cities, even the failed attempt to assassinate Margaret Thatcher. Passions about whether there should be a united Ireland or whether the Six Counties should stay in the United Kingdom go very deep and they could be re-ignited at any time.

Perhaps it is fitting to leave the last word to Alan Black, a man with more reason than most to never want to risk a return to the Troubles: "This is what Brexit is going to do to us if they put a hard border up. You're going to get the hard men coming out of the woodwork and they're going to start attacking border posts, which means sending police to protect them and army to protect the police . . . It's unthinkable, it's going to be a disaster."

That disaster is avoidable, but only if we all wake up to the real dangers of a no-deal Brexit – and fast.