Long queues at Dover may be the first sign of what it means to live outside the European Union

Perhaps Britain will find, in the uncertain new world it has chosen to live in, that it cannot implement Boris Johnson’s policy on cake – 'pro having it and pro eating it'. Easy as a backbencher, or even mayor of London; not so easy as Foreign Secretary

The hundreds of people trapped for up to 14 hours in their cars en route to the port of Dover deserve our utmost sympathy – many, of course, for a traumatic start to their summer holiday. The marathon delays are being portrayed as a blip caused by understaffing and underfunding by France of its border posts in Dover, and understandably tougher security checks following the horrific terrorist attack Nice. However, the scenes in and around Dover might also signal something else: the start of what Brexit could mean, in practical terms, for a more isolated Britain.

Now that we have turned our backs on the other 27 EU members, can we really expect them to co-operate so closely with us, on a whole raft of issues including immigration, as if nothing had changed? We may find that France and other EU nations see little reason to resolve problems such as the chaos unfolding in Dover either quickly or efficiently.

It is true that Francois Hollande, in his talks with Theresa May in Paris last Thursday, promised that UK border controls would remain in Calais rather than move to Dover, as some French politicians and Remain campaigners warned during the referendum campaign. But with a French presidential election next spring, and the National Front possibly on the verge of a breakthrough, the Anglo-French agreement may well come under pressure again. At one level, we could hardly blame the French for putting little priority on a border security arrangement that helps us far more than it helps them.

Patrick McLoughlin, the Conservative Party chairman, denies that events in Dover show the UK is being punished for the Brexit vote, pointing to the importance of tourism to both countries. But perhaps Britain will find, in the uncertain new world it has chosen to live in, that it cannot implement Boris Johnson’s policy on cake: he memorably said he was “pro having it and pro eating it.” Easy as a backbencher, or even mayor of London, but – as he will discover – not so easy as Foreign Secretary.

Johnson is already taking the message around the world that the UK has not pulled up the drawbridge and is open for business. But adopting what appears, and indeed threatens, to be an isolationist stance in an increasingly inter-connected world, and one in which power blocs matter, is bound to have practical implications for Britain. If the queue at Dover passport control is the first, it will certainly not be the last.

Of course, Brexit may have many positive impacts too. Eventually, our trade with non-EU countries might be stronger than it might have been if we had stayed in the EU. Perhaps, by playing a positive role in Nato, the United Nations and in the world's trouble spots, we will convince other countries that we have not turned our back on them and will still enjoy clout on the global stage.

However, the snakes of traffic outside Dover are a reminder that we cannot expect life to carry on as normal after Brexit.

No doubt May and her Government will feel some pressure as people realise the downsides of leaving the EU. It is revealing that the Prime Minister plans to launch several policies to flesh out her “opportunity for all” domestic agenda over the summer, in the hope of achieving her goal that Brexit will not define her government or the country.

She will have her work cut out to prevent that; Brexit will surely dominate our politics and national life for years to come.

There may be one other significant effect of choosing to go it alone. Our leaders can no longer expect to insulate themselves from peoples’ ire by blaming the EU, a convenient scapegoat for UK politicians in recent decades. Indeed, constant “blame Europe” carping by both Conservative and Labour figures over the years was surely a fundamental reason why a majority of people voted to withdraw.

Very few prominent figures in either party had the courage to make a positive case for EU membership. This begs an important question: who on earth will the politicians blame after we have left the EU?