“Current policy: to break the whole thing up. So we had to get inside. We tried to break it up from the outside, but that wouldn’t work. Now that we’re inside we can make a complete pig’s breakfast of the whole thing: set the Germans against the French, the French against the Italians, the Italians against the Dutch. The Foreign Office is terribly pleased. It’s just like old times.”

I couldn’t resist starting with a quotation from Sir Humphrey in the brilliant series of Yes Minister 30 years ago. Tongue-in-cheek it may be. But time has, if anything, made it even more relevant.

The vexed relationship between Britain and the European Union long predates Prime Minister David Cameron. Despite Winston Churchill’s much-quoted 1946 speech calling for a “United States of Europe”, it has troubled Britain’s major political parties for decades.

It was a Labour government that decided in 1950 to stand aside from Europe’s first fumbling efforts to form a coal and steel community. It was the Conservatives (the Tories) who took Britain into the European Economic Community in 1973. And it was Labour, under masterful tactician Harold Wilson that then staged a renegotiation to draw the sting from Eurosceptic elements in his own Labour party before holding (and winning) a referendum in 1975. The two parties have since alternated between bouts of Euroscepticism and (brief) bursts of enthusiasm.

Cameron began his time as Tory leader pledging that he did not want to be “banging on” about Europe. But he did not reckon with his own right wing.

He made his pledge to call hold a referendum – in the face of a strongly Eurosceptic threat to the party by the insurgent United Kingdom Independence Party as well as to hold together his divided party – without thinking through the consequences of his actions.

While UKIP was vanquished at the last general election, his promise of an in/out referendum has opened a Pandora’s box which is tearing his party apart and could well see him being forced to resign in four months’ time – whatever the outcome of the referendum.

He chose to manage the unmanageable and the consequences of that decision could well see the end of his premiership.

I have many Eurosceptic friends, many in their 60s and beyond. There are also many Tory MPs sitting on the backbenches – perhaps half the parliamentary party – who are children of the Thatcher generation (“No. No. No” to a federal Europe, she said in 1990, leading to her Foreign Secretary’s resignation and her eventual downfall).

The older hark back to a different era and a different reality. The younger have illusions – fantasies – about a largely imaginary “Anglosphere”, or some Tory version of “Britain Alone that the United Kingdom can somehow leave Europe, pull up an imaginary draw-bridge and restore a 19th-century ideal of parliamentary sovereignty. I call this delusion “terminal nostalgia”, an emotional, unrealistic wish for a world long gone.

Of course, there is much that is wrong with the European Union To its critics, the EU always lacked democratic legitimacy. All attempts to make good the “democratic deficit” have failed.

Trust in the EU is at an all-time low. Even the once committed Dutch are pressing for a referendum to be called on their EU membership.

Widespread disagreement between 28 disputatious states has led to the EU appearing weak and divided and its voters disillusioned. Squabbles, stifling bureaucracy and complacency have marked the last decade. The poisoning of domestic politics right across the Union has hampered decision-making by governments. The north/south economic divide and east/west democratic fissures are big and growing. Making the bold and wide-sweeping reforms needed to tackle the instability caused by the migration crisis and to mend the deeply flawed currency union have added to the feeling of a punch-drunk continent lurching on the ropes.

To leave now would be an abdication of responsibility. Britain will never love the EU but its interests – and the interests of the west and Europe itself – are best served by trying to reform Europe from within

But, even setting aside the impact which a vote to leave would have on Britain’s economy and security and the almost certain prospect of the break-up of the United Kingdom (with Scottish independence inevitable and Northern Ireland dangerously unsettled), to opt out of the EU now would have even wider repercussions.

The idea that Britain can separate itself from Europe is a romantic illusion. The future of Europe without Britain would be one of escalating instability – from which the British people themselves would, of course, not be immune.

It would lead not only to Britain relinquishing all influence over the terms of its future relationship with its main trading partners and jeopardise London’s future as a financial centre, but also – more importantly – undermine the security and stability of Europe itself.

The impact of British withdrawal on European unity and the West would be far-reaching. This is a dangerous time in world history. The impact on 21st century history of a major fracture within Europe is impossible to calculate. But I believe it would reverberate through this century. Britain’s exit would rock the west to its foundations – not just Europe and the Americas, but Japan and Australia too.

Britain is Europe’s second largest economy. It is the fifth largest economy in the world. It is Europe’s biggest defence power and the fifth biggest in the world. It is the second most powerful member of NATO after America. It occupies one of the five permanent seats on the UN Security Council.

Eurosceptics cite these strengths as evidence that Britain could go it alone, overlooking that outside the EU it would be on the sidelines, notionally sovereign and independent, but in fact still constrained by rules it would have no role in formulating. Those who make this case, and set much store by British friendship with America, should ask themselves how Washington would view a major fracture within democratic Europe.

How would Putin view the news? Imagine the glee. How would Daesh jihadists broadcast this new example of disunity in the west? Would they take fright – or heart – that Europe was dividing?

Britain’s breakaway would signify a collapse for the whole. It would carry profound implications for more than the balance of power in the world.

It would also affect the battle of ideas and values, a battle which is turning critical in the face of the jihadist threat and a revanchist Russia.

Without Britain, the future of the EU looks fragile. Without it, the disintegration of the EU could well occur.

Populist parties urging their countries to leave the EU or the eurozone, or both, have multiplied. France is no longer a counterbalance to Germany. Italy is struggling. Spain is still finding its democratic feet. The Visegrad countries are going it alone.

With Britain’s great weight removed, the centre of gravity of the whole would shift and could topple the whole structure. History would be right to cast Britain as the accomplice to the wreck.

To leave now would be an abdication of responsibility. Britain will never love the EU. But its interests – and the interests of the west and Europe itself – are best served by trying to reform Europe from within, rather than taking a gigantic leap into the unknown and bringing the whole structure crashing down.

This alone should cause the British people to vote to remain. We must pray for that renowned British pragmatism and national self-interest to prevail.

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