Calais may continue to haunt David Cameron's dreams

It is a journalistic cliche to label some difficult problem or another as a "nightmare" for a politician - but the very visual impact of the roiling, repetitious, nightly chaos in Calais could well haunt the prime minister's bedtimes.

The sight of "swarms" of aliens shaking the fence night after night, like the opening sequence from some zombie movie, must have a haunting quality for Mr Cameron, who promised to take back control of Britain's border.

The PM 's quotidian helping of humiliation may have been delivered in smaller portions in the last few days.

However, the fact remains that this is not a natural disaster or an unforeseen emergency but the result of multiple political failures, policies that don't work piled on top of each other like a stack of lorries along the M20.

While by no means all the failures should be laid at the door of our government, its reaction, tellingly guiltily, both laggard and over-hasty, paints a picture.

Its responses often seem like a headline in search of a policy.

More sniffer dogs are ordered but security considerations prevent ministers saying how many.

A surge of private security guards is ordered. It takes three days to decide a "surge" means 100.

Which is why it is worth looking in detail at the many components of this crisis and to ask if a little policy pressure at any of the choke points could kill it.

But first, the background. The government's desperation is because of its promises on immigration.

That has everything to do with the huge increase in legal immigration from the European Union.

Polish plumbers, Estonian baristas and Portuguese pluckers of Christmas turkeys have little to do with the sort of desperation we see nightly across the tunnel.

Except that they, and the rise of UKIP, meant that the rise of immigration is an issue of acute sensitivity for the government. It is seen as political suicide to allow more people in.

This is not a domestic problem, but let us start at home.

The migrants congregate in Calais because of the lure of Britain and the strength of its island border outside the Schengen area.

A strong economy and the English language must be part of the magnet and a government would have to be even more worried about Calais than this one to force us all to speak Icelandic and engineer a second banking crisis to put off would-be immigrants.

Ministers are not much more likely to consider French suggestions of tighter labour regulations and ID cards to close down the black economy.

They are trying to convince would-be migrants that when it comes to illegal immigration, they are indeed the nasty party.

But ill-thought-out plans to force landlords to evict those refused asylum are unlikely to do the job.

If the word has gone out in the Sahel that Britain is a soft touch, it will take more than a few headlines to undo that impression.

It is, anyway, a bit of a misconception that the UK is so very much more attractive than any other land.

The migrants congregate in France because Britain doesn't want them, and being outside the Schengen Agreement and an island allows us to make that rejection a reality.

Far more would-be asylum seekers go to Sweden or Germany, partly because they do not have the same watery border and partly because they are more welcoming.

A Swedish minister told me that if you look at the real figures, the European Union's crisis consists of the equivalent of an island of 1,000 people working themselves into a lather about the arrival of one extra person per year.

One obvious answer would be for Britain to take the paltry 5,000 people waiting over the water and solve the crisis at a stroke.

The obvious retort to this is that it would only encourage even more to come.

This brings us to the next obvious failure. It may be sporting to allow would-be migrants to congregate en masse and chance their luck on getting through to England. It is scarcely logical, though.

A coherent policy would dictate they should be granted asylum or deported.

But the French are unwilling to take up this burden, given that the UK is the migrants' destination.

If asylum is off the agenda, so, it appears, is deportation.

Whatever the logic, returning people to the horrors of civil war in Syria or slave labour in Eretria cannot be high on the agenda of things politicians want to do.

There is a clear reason the would-be migrants can make it to Calais. Under the Schengen Agreement, the continental European Union has effectively abolished borders.

The former Home Secretary Jack Straw suggested to me the other day that the borders should go back up.

Given the thousands of miles they cover, and the cost to the EU's nations which that would entail, that seems extremely unlikely and unattractive.

But it is more than possible that here and there, a few bits and pieces of sporadic barbed wire will be erected, creating a few Calais-like scenes, with added futility.

Europe's problem begins on the shores of the Mediterranean.

Letting the would-be migrants drown is a dreadful option, and that hard-headed policy was soon abandoned.

Still, patrols have been cut to avoid giving the impression that a leaky boat is a passport into the European Union.

The most egregious failure is the inability to develop a European policy to respond to a European problem.

In a very uncommunicative way, many nations seem pleased to see this as a Greek or Italian problem.

It hardly needs to be said that ending war and dictatorship and poverty in the countries from which people flee would help end this ongoing crisis. Good luck with that.

Setting out each of the potential points where the crisis could be solved shows how difficult this is.

Every solution leads to another problem, potentially worse than the one it solves.

US President Barack Obama used to say that if it was easy, a problem wouldn't end up on his desk - it is tough at the top.

The Schengen Agreement led to the creation of Europe's borderless Schengen Area.

The treaty was signed on 14 June 1985 by five of the 10 member states of the European Economic Community near the town of Schengen in Luxembourg, but wasn't implemented for a further decade.

It proposed the gradual abolition of border checks at the signatories' common borders.

The Schengen Area operates very much like a single state for international travel purposes.

There are external border controls for travellers entering and exiting the area and common visas, but no internal border controls.

It currently consists of 26 European countries covering a population of more than 400 million people. The UK and Republic of Ireland have opted out.

The same is true for the prime ministers and presidents of the European Union.

As German Chancellor Angela Merkel likes to say, where there's a will, there's a way.

But there is little will to take these very hard decisions.

This crisis looks, for all practical purposes, insoluble, without end.

Mr Cameron's nightmare may recur, as nightmares tend to do.