This is the worst possible time for Britain to consider leaving the EU – or for Scotland to break with Britain.

The EU is an unfinished project of European states that have sacrificed part of their sovereignty to form an ever-closer union based on shared values and ideals. Those shared values are under attack on multiple fronts. Russia’s undeclared war against Ukraine is perhaps the most immediate example but it is by no means the only one. Resurgent nationalism and illiberal democracy are on the rise within Europe, at its borders and around the globe.

Since world war two the European powers, along with the US, have been the main supporters of the prevailing international order. Yet, in recent years, overwhelmed by the euro crisis, Europe has turned inward, diminishing its ability to play a forceful role in international affairs.

To make matters worse, the US has done the same, if for different reasons. Their preoccupation with domestic matters has created a vacuum that ambitious regional powers have sought to fill.

The resulting breakdown of international governance has given rise to a plethora of unresolved crises around the globe. The breakdown is most acute in the Middle East. The sudden emergence of the Islamic State in Iraq and the Levant, or Isis, provides the most gruesome example of how far it can go and how much human suffering it can cause.

With the Russian invasion of Ukraine, military conflict has spread to Europe. Two radically different forms of government are competing for ascendancy. The EU stands for principles of liberal democracy, international governance and the rule of law. In Russia, President Vladimir Putin maintains the outward appearance of democracy by exploiting a narrative of ethnic and religious nationalism to generate popular support for his corrupt, authoritarian regime.

As a major power and global financial centre, Britain ought to be centrally involved in crafting a European response to this threat. But like the US and the EU itself, Britain has also been distracted by internal matters. Conservative Prime Minister David Cameron has been persuaded by anti-European zeal – not least within his own party – to put UK membership in the EU to a vote in 2017. A poll on Scottish independence is only days away. Just when Britain should be confronting grave threats to its way of life, it is preoccupied with divorce of one type or another.

Divorce is always messy. A vote for Scottish independence would weaken – in political and economic terms – both a truncated UK and Scotland. An independent Scotland would be financially unstable, especially if threats to renege on debt repayments were carried through.

For Scotland and the rest of the UK to enter into a currency union without a political union, after the euro crisis has demonstrated all the pitfalls, would be a retrograde step that neither side should contemplate. Yet without it, an independent Scotland could not benefit from the low interest rates that a strong pound has brought. These considerations ought to outweigh whatever possible benefits independence might bring.

Yes, there are significant policy differences between Scotland and the rest of the UK. There is a more left-leaning approach to many issues, notably education, north of the border. But Scotland would be better placed to attain its political goals as part of a united Britain that is part of the EU.

The same applies to a British exit from Europe. Policy differences can be mediated. A divorce would weaken the UK. Those who call for separation seem to have forgotten that Britain currently enjoys the best of all possible worlds. Being part of the EU but not part of the euro allows the UK to enjoy the trading benefits without the currency constraints.

Furthermore, Britain has always played a balancing role between hostile blocs. Its absence would greatly diminish the weight of the EU in the world.

The EU has proved to be the best guarantor of peace and human security since the end of the second world war. The importance of preserving the shared values underpinning a whole way of life far outweigh any possible advantages of independence. The difficult times we are facing call for increased unity, not divorce.

Only if Britain fails to resolve its differences with the EU, and if the pro-European Scots (having voted to remain within the UK) thus find themselves unwillingly excluded from Europe in 2017, would there be just cause for Scots to call for a new referendum. If it comes to that, Scotland will be in a different position – one that could legitimise a split.

But to vote for independence from the UK now would be to prematurely surrender Scottish leverage in London, and Britain’s leverage in the world.