Can we avoid huge economic upheaval if we quit the EU? asks Canterbury consultant Martin Roche

We need be under no illusions about the potential consequences of an IN/OUT referendum on EU membership.

For the purposes of this article, let’s assume the Conservatives have won an outright majority in the 2015 General Election. And let’s assume the other 27 EU states (Croatia, the 28th EU member, joins in June) agree to hear David Cameron as he puts his case for the UK to have certain powers returned to Westminster.

Our friends and allies listen carefully and politely but after a year or two of discussion, frustration and some harsh words from all directions, David Cameron returns with about half of what he set out to get.

He advises the British people to cast their vote to stay in the EU at the referendum.

The Prime Minister asserts he has secured the best possible outcome – we keep our guaranteed access to the single market and the sovereignty of the Westminster Parliament is once more in the ascendency. All that remains now is for the people to follow their political leaders and put a big X in the IN box.

Ah but as Robert Burns wrote, the best laid plans of mice and men “gang aft agley” (“often go astray”). Let’s imagine that the political forces wanting Britain to quit the EU run a brilliant campaign which sees a majority of UK voters come down on the OUT side. The people have spoken and not long afterwards, Parliament passes legislation disentangling the UK from Europe.

We are now on our own. The Europeans say how sad they are that Britain has divorced itself from 27 nations that held it in high regard and promise eternal friendship.

In reality, the Europeans feel bruised, rejected and in no mood to do Britain any favours. Washington is aghast and begins to cement a new relationship with the most powerful EU nations. Germany, France, Italy and Poland walk a little taller in the world.

Unemployment creeps up as trade with the EU falters. The single market now closed to the UK, national and state governments stop inviting British companies to tender.

Expatriate Britons, having lost automatic rights to work and live in any EU country, drift back.

It is one thing to win political legitimacy for EU withdrawal but another to imagine that an Out vote will somehow endorse the political philosophy of its proponents. Let the debate begin.

Martin Roche runs the Canterbury-based consultancy Anchor Reputation Management. EU clients account for 70% of turnover.