ON NOVEMBER 24TH an inflatable dinghy capsized off the coast of Calais, France. At least 31 people drowned in the frigid water; 26 were rescued by the French coastguard. They were trying to get to Britain via an increasingly popular but perilous route. After years of effort by authorities trying to stop migrants arriving from the continent stowed away in lorries, rising numbers have turned to small boats. On November 11th the total arriving on the Kent coast hit 1,185, a record.

The deaths turned a front-page political row into a tragedy. Conservative MPs say that, even as Parliament is consumed with scandal about second jobs, contacts by constituents concerned about immigration in small boats outnumber those about sleaze. Nearly 60% of Conservative voters say that immigration or asylum is one of the top three issues facing the country. Nearly 80% say the government is handling the issue poorly.

This is alarming for Boris Johnson, the prime minister, who campaigned for Brexit on a promise to “take back control” of Britain’s borders. On November 22nd Nigel Farage, the former leader of the UK Independence Party and the Brexit Party, said the rising number of migrants might lure him out of retirement. The resurgent threat on its right flank horrifies the government. Mr Johnson has ordered a review aimed at stopping small boats from attempting the Channel crossing.

But this is easier said than done. In the run-up to the 2019 election Priti Patel, now home secretary, said she would halve the number; instead it increased nearly 14-fold. Migrants set out in the face of extreme risks, and for reasons that no destination country can control, such as war, famine and poverty. Aid, which donors hope may keep recipients at home, can instead give them the means to leave. Many in Calais’s camps want to go to Britain because family members are there, says Frances Timberlake of the Refugee Women’s Centre, an aid organisation. Others want to move on because of poor conditions. The European Council on Refugees and Exiles, an NGO network, estimates that fewer than half of applicants for asylum in France in 2019 were provided with housing.

Those migrants who make it to Britain’s shores have the right to seek asylum. As an EU member Britain could invoke the Dublin Convention, a deal struck in 2013 that requires claims to be made in the EU country of first arrival. In fact, returning those who moved on proved difficult. But in any case, Britain is no longer covered.

Many of the 25,000 migrants who crossed the Channel this year are likely to qualify for asylum. The Home Office does not regularly release data on applications, but an analysis by the Refugee Council, a charity, found that arrivals by boat tend to originate in countries with high approval rates. Between January 2020 and May 2021 Iranians were the biggest group. Their approval rate before appeal is 67%, compared with 52% for all nationalities. For Syrians, the fourth-biggest group, it is 88%.

Since the Brexit referendum voters have become less concerned about immigrants arriving for work or family reunification. But 56% have an unfavourable view of those who enter illegally. Other routes are, however, largely closed. Britain has no humanitarian-visa scheme for asylum-seekers. In August the Home Office announced a programme to resettle Afghans who had worked for Western countries and charities. It has yet to get off the ground.

Ms Patel has considered using Britain’s border force to push boats back into French waters. But that may be illegal under maritime law and anyway requires French co-operation, which is unlikely to be forthcoming. Another idea is to hold asylum-seekers offshore while their claims are processed, as Australia does on the Pacific island of Nauru. The Home Office says that it is in talks with Albania’s government—a claim its prime minister has denied.

The centrepiece of Ms Patel’s plans is a draft nationality and borders bill. It would create a two-tier system, with arrivals through informal routes granted less time to stay and denied opportunities for family reunification. It has faced sharp criticism. According to a legal opinion commissioned by Freedom from Torture, an NGO, some parts violate international law. That is unlikely to stop the bill passing, but may delay it in the House of Lords. And in any case, there is little evidence that the harsh asylum policies influence migrants’ choices. An assessment of the draft bill by Home Office concluded that evidence for the effectiveness of deterrence was “limited”. Researchers who interviewed migrants who crossed the Mediterranean during the crisis of 2015 came to a similar conclusion.

Former Home Office officials say the best way to cut arrivals by boat is to work closely with France. In 2016 the two countries managed to dismantle la jungle, a camp in Calais that housed thousands. Some residents were granted asylum. Britain recently unblocked more of the £54m ($72m) it has promised to spend helping the French patrol the coast. But the French authorities argue that they are already doing all they can to stop departures. So far this year 31,500 migrants have set off, they say, with 7,800 rescued and brought back to France. On November 23rd they arrested 15 people connected to a people-smuggling ring that had brought 250 migrants across the Channel for a fee of €6,000 ($6,700).

Increasing cross-channel co-operation would require trust, which is in short supply. In response to the latest drownings the French president, Emmanuel Macron, declared that “France will not let the Channel become a cemetery”. But the two countries are embroiled in Brexit-related rows, notably over fishing permits. Mr Macron is fighting for re-election in April and, although fishing permits and small boats barely feature in the public debate, he needs to be seen standing up for French fishermen and local interests.

Mr Johnson, too, is keenly aware of voter sentiment. Seen from countries such as Greece and Italy, which are more accessible from some of the world’s trouble spots, the numbers making it to Britain are tiny. And the cross-Channel flow is likely to subside as the weather grows colder and the seas choppier. But at least ten migrants have died in the past few weeks, not counting the latest tragedy. British politicians have been put on notice that if the numbers arriving, or dying en route, pick up again in the spring, they should expect pushback at the ballot box.