I have not become the King’s First Minister in order to preside over the liquidation of the British Empire.

So Winston Churchill declared in 1942. Seventy years on, David Cameron no doubt feels something similar. Yet three recent developments appear to signal the downsizing of Britain’s role in the world: next year’s referendum on Scottish independence, as laid out in this week’s White Paper; a UK referendum on EU membership, promised for 2017; and the Commons vote against action in Syria.

These developments are puzzling, as is their coincidence. For almost 50 years the political establishment has been confident in the longevity of the Union, unabashed at intervening abroad, and broadly united in believing that Britain has a crucial role inside Europe – a role that both furthers its economic interests and bolsters its global influence. But times have changed: power political considerations are for the first time being genuinely challenged by a democratic imperative articulated from below.

The old common sense opinion that the UK’s place is within Europe and that Scotland’s is in the UK, was underpinned by an elite-mass consensus on the legitimacy of Britain’s role in the world – a consensus that in turn motivated an interventionist foreign policy. This common sense no longer applies. For eurosceptics and pro-independence Scots alike, neither Europe nor the UK represents an unambiguously positive political project that trumps the benefits of going it alone.

This week saw the publication of the SNP white paper laying out the case for Scottish independence. Pro-independence campaigners highlight the paradox of Scotland being governed by a party that won only one of the 59 parliamentary seats north of Hadrian’s Wall. Calls for a return of democratic control are therefore an attack on the status quo behind unionism and EU membership.

The EU’s “democratic deficit” has long been a concern. But its insistence on ever-greater macro-economic control in order to solve the Eurozone crisis makes integration an even harder sell to a sceptical British audience.

The upcoming referendums thus pit political considerations about the UK’s role in the world against democratic ones about the UK itself. To paraphrase international relations theorist Hans Morgenthau, David Cameron is “democratic man versus power politics”.

The Prime Minister's Office

World power or democratic legitimacy?

Rather than criticising Cameron for jeopardising Britain’s role in the world, we should congratulate him for not simply dodging domestic demands for greater control over Britain’s external relations. For decades, Labour and Tory leaders alike have arrogantly discounted the genuine fears of those who want a thorough accounting of the benefits and costs of EU membership. By contrast, Cameron has promised an open and frank debate on what membership gives to those living in the UK. This should be welcomed. At present, the alternative position espoused by many anti-EU Tories and UKIP is merely empty rhetoric about self-government tinged with xenophobia, and not the positive vision of Britain’s future they pretend it is.

Cameron should also be applauded for facilitating a civil but impassioned debate on what membership of the United Kingdom provides to the Scottish. Like the independence from the EU campaign, the “Yes” campaign in Scotland remains vague in important respects, and its economic forecasting is optimistic to say the least. But the cross-party case against independence should not take a fear-mongering tone about the risks, economic and otherwise, that an independent Scotland would incur.

Rather, it should reflect – and reflect on – what is really at stake in the Scottish referendum: the viability of the United Kingdom as a political project. There is no doubt that an independent Scotland would be viable. It might not be rich or influential, but as many have argued, the whole point of the push for independence is that wealth and international position are not everything. Instead, the “No” campaign must show what the UK gives its Scottish citizens that is worth holding on to.

But these developments do not simply concern the UK; they also pose a similar quandary for Britain’s allies, especially in Washington. For its part, the United States’ response should honour the primacy of legitimacy in its vision of international order. US foreign policy may be best served by an Atlanticist Britain inside the European Union, but Washington should support Britain’s debate over Europe – and Scotland’s over independence.

The unbottled genie

There is no guarantee against the British electorate opting to exit Europe, or the Scottish electorate choosing to leave the United Kingdom. But the referendums must be seen as opportunities for democratic engagement in search of political legitimacy, rather than as risks to be avoided in the service of an increasingly unappealing status quo.

Spooked by the unbottled genie of euroscepticism, Cameron might well demur on the EU referendum. He might also lead a negative campaign aimed at scaring the Scots into remaining part of the UK. He must do neither. He should honestly and firmly set out the case for the United Kingdom in Europe and Scotland in the United Kingdom.

Crucially, this is the best course for both democratic and power political reasons. Democratic man versus power politics is a false alternative. As realist scholars such as Morgenthau recognised, power politics without legitimacy is empty, if not tyrannical; legitimacy without power politics is weak.

The Commons vote on Syria is the case in point: despite howls of an end to Britain’s history, the vote represents nothing of the sort. Rather, it has shown that in a democratic era, true legitimacy can only come through the ballot box. Although opening up these questions to voters feels dangerous to those standing against a British exit from Europe or a Scottish exit from the UK, it would be more dangerous yet to ignore calls for change.