If Boris Johnson wants to stop the Channel crossings, he has to work with Emmanuel Macron

The prime minister added to the heatwave with a blast of hot air yesterday. He said he wanted to “look at the legal framework” governing people crossing the Channel in small boats. He spoke as if his government has the power unilaterally to stop this traffic, thus exposing the folly of UK isolationism.

As leader of the Leave campaign in the Brexit referendum, he has to pretend that leaving the EU gives him more power to control our borders. As a former foreign secretary, he should know better.

The situation was described with commendable clarity by David Miliband, another former foreign secretary, who offered his textual analysis of the government’s message: “The first sentence is ‘take back control’. The second sentence says: ‘We’ve got to get the French to do more.’ And so you’re immediately into a reality of the modern world that ... you rely on other people doing things.”

There are no laws that the UK parliament can pass that would allow our authorities to “send them away”, as Boris Johnson puts it, once people cross into UK territorial waters. It ought to be obvious that any attempt to do so would require the cooperation of Emmanuel Macron, the French president.

If Mr Miliband had wanted to be more brutal he could have spelt out how it works. We pay the French to police their coastline. They have little incentive to keep large numbers of people who want to come to the UK in their country, but have been persuaded over the years that enforcement and dispersal is better than allowing makeshift slums such as the Calais “jungle” to grow on their northern coast.

Paradoxically, perhaps, Brexit makes it harder to ask the French to do our border control for us. First, because they are less likely to feel that we are part of their common endeavour with the rest of Europe to manage migration; but second, because we will after the end of the year cease to be bound by the EU Dublin convention, which includes the presumption that refugees should seek asylum in the first safe country to which they come.

The Independent has always argued for a compassionate policy towards refugees and a self-interested policy of welcoming economic immigration. That means fair rules, which have to be enforced, and that means, in turn, working with our neighbours. No one wants to encourage people to take to the sea in dangerous dinghies, however sympathetic we might be towards their desperation. That means stopping the journeys at source, in France, and preferably before would-be migrants even make their way to the coast, by cracking down on the trafficking gangs.

We suspect that when the prime minister’s hot air about changing the law is blown away, and when the home secretary’s rhetoric about calling in the navy is revealed as empty words, this Brexiteer government is going to end up trying to reinvent the partnerships with other European countries that were once organised through our membership of the EU.