But that is not to say that the IRA campaign, at least initially, also moved the Overton window as to what was deemed possible and necessary by senior policy and decision makers. For one thing, the unionist bastion of Stormont was dissolved and the UK government took much more of a direct interest in and responsibility for running N. Ireland.

But while initially welcomed by nationalists in NI as a protection from unionist security forces, this quickly morphed into an army of occupation employing Kitson style counter-insurgency tactics as had been used in the colonies.

The Irish government also became much more directly involved, negotiating directly with the British government on behalf of nationalists - initial with a very hostile British government, but gradually cooperation between the two governments improved because of the multiple relationships built up through joint EU membership, and the realisation, on the British side, that the war was never going to be stopped without active support from the Irish government.

However, very early on, the law of diminishing returns kicked in to the point where IRA violence merely stiffened unionist and UK government resolve and made political concessions more and more difficult. Ultimately it became completely counter-productive, at which point the IRA leadership started to looking for a way out of the war without losing too much face.

But the end of the IRA has also had a negative effect. Whereas during the GFA negotiations and for many years afterwards UK/Ireland relations became better and better - culminating in a very positively received visit by the Queen in 2010 - relations between the governments have become progressively worse since Brexit, and are now at their lowest point since Bloody Sunday.

The parallel I draw is with the demise of socialist parties in the West after the fall of the Iron Curtain.  Once the Cold War was over, capitalists and their political parties no longer had to worry about the risk of social revolution at home. They became increasingly brazen in destroying trade unions, workers rights, and promoting ever more unequal policies.

The Tory party now doesn't care about the risk of re-igniting the Troubles. It doesn't care about antagonising the Irish government or the EU. Only a humiliating defeat in a serious trade war will, I think, bring the UK governing class back to their senses.

So the EU needs to be aware that the current dispute over the Protocol is about much more than customs technicalities. It is about the UK proving it is the Equal of the EU and can do more or less whatever it wants without effective sanction.

If we don't want large scale violence to break out in N. Ireland all over again, the EU needs to be absolutely ruthless in its defence of the international legal order and in protecting the interests of its local member state most effected.

Index of Frank's Diaries