Hours before the disaster, the French police had stood and watched, doing nothing to prevent a rubber dinghy packed with around 40 migrants from launching into the English Channel for the perilous journey to Britain.
An alarming photograph showed police officers watching the people smugglers putting their human cargo to sea and failing to intervene.
That boat, launched at 5am from Wimereux, a seaside town just north of Boulogne, made it to Dungeness in Kent hours later.
Another boat that embarked a few miles away, nearer to Calais, did not.
Just after 1pm, a French fisherman came across the horror of bodies - 15 at first glance - floating in the sea. Ominously, there was no boat to be seen. France’s interior minister would later describe the vessel that capsized as “very fragile”, adding by way of explanation: “It was like a pool you blow up in your garden.”
In freezing temperatures - the water was reckoned to be no more than 10C - survival time would be limited, even for those with life jackets.
The sea had been calm and the wind largely still; with winter approaching, yesterday must have seemed like a good day for migrants to reach Britain.
This year, almost 26,000 men, women and children have safely negotiated the Dover Strait, the world’s busiest shipping lane.
They were the lucky ones. Yesterday showed that the luck has to run out.
The fishing vessel that found the corpses put out a mayday signal, triggering a huge emergency response. French and British coastguards, naval ships and helicopters raced to the scene. What they found were more bodies, including at least one girl and five women, and just two survivors - although they were not expected to make it. “Their days are numbered,” said France’s interior minister.
Last night, the official death toll stood at 31, with at least one other passenger on the dinghy unaccounted for. It is thought to be the greatest single loss of life in the Channel since the war.
Matt Cocker, a Dover fishing skipper on his boat Portia, had heard the mayday call. He was too far away to help but listened to the tragedy as it unfolded.
“A French fishing vessel must have gone past and they alerted their coastguard. They initially reported 15 bodies in the water,” he said, speaking from out at sea. “The scenes must have been desperate. Awful. Picking bodies out of the water for anyone is the end of things and you don’t want to be doing it.”
His onboard radar did not appear to show other boats in the immediate vicinity of the stricken dinghy - about six miles north of Calais in French waters - suggesting, he said, it had not been hit by a larger vessel.
More likely the boat was overloaded and either split or sank under the weight of its passengers. One big wave might have been enough to force it under.
“These are really cheaply-made flimsy craft. You can barely call them boats,” said Mr Cocker. “The sea was absolutely flat, with probably about 30 migrant boats taking advantage of the best weather for days to cross. But the traffickers put them in cheap plastic inflatables. They’re not proper boats. They overload them and they split and deflate, and the people end up in the water. They often don’t have life jackets. They don’t stand a chance.”
Earlier in the day, Nicolas Margolle, a French fisherman, said he had seen two small dinghies, one with people on board and another empty. It is unclear if the empty boat was the stricken craft.
With at least eight dinghies making the crossing successfully yesterday, it remains unclear whether Mr Margolle was witnessing the disaster unfold and hadn’t realised it.
Mr Margolle said that another fisherman had later called rescue services after seeing 15 people floating motionless nearby, either unconscious or dead.
Three helicopters and three boats were deployed in the initial search, local authorities said. That included a British helicopter from the Maritime Rescue Coordination Centre in Dover along with a French naval helicopter and patrol vessel, a police boat and a lifeboat.
It appears that two bodies were pulled out of the water, still conscious but suffering badly from hypothermia. The survivors, should they pull through, will be key to piecing together what happened.
Gerald Darmanin, the French interior minister, said at a hastily arranged press conference that search operations would continue through the night, although few had hope of finding anyone alive.
Four people, accused of being the traffickers who had sent the migrants to their deaths, were arrested in connection with the tragedy.
Mr Darmanin said the victims had ended up in the water after the boat had sunk. “It was a very fragile boat,” he said., “When life boats arrived, it was already as deflated as a blow-up paddling pool in a garden.”
He said that on the blackest of days, 255 migrants had made it safely across the sea and, defending his country’s record, that 671 were stopped from doing so or arrested. An army of 780 police and gendarmes were monitoring the northern French coast, he said.
“What happened today to our knowledge is that 31 people were drowned between Calais and Dunkirk,” he said. “There are two people who have been saved, and their days are numbered.
“Amongst the 31 dead, as far as we know five were women and one was a little girl. We don’t have any more information with regards to those people. We will carry on searching in the hours to come to see if there are any more people.”
The migrants will have paid a few thousand euros for a voyage in a death trap, likely coming from Iraq, Afghanistan, Africa or Asia. Their goal, having finally reached northern French shores, was the UK.
Jean-Marc Puissesseau, the president and chairman of the ports of Calais and Boulogne, called for heads to be banged together in the UK and EU to find a solution, warning that more fatalities would inevitably follow.
“The sea is very, very cold, there is little chance of survival,” said Mr Puissesseau. “Traffickers are assassins. We were waiting for something like this to happen.”
“Even if the sea is not looking so rough, in the middle there are always many waves. It is dangerous. That can happen again because they try everything to get to your country. That’s why I am very upset. I don’t know what to do.”
By yesterday afternoon, the corpses were starting to arrive at the Paul-Devot quayside in Calais where the bodies of recovered migrants are usually taken. Around 20 emergency services vehicles along with port authorities were in situ. Leave for firefighters, who were needed in the operation, was cancelled.
Police cordoned off the area and a special motorised hoist was brought to the scene to bring the victims on to dry land. As the bodies were being removed, the blame game was starting.
Natacha Bouchart, the mayor of Calais, suggested Boris Johnson was at fault, but in the UK, responsibility lay for many with the French authorities.
“Part of the problem is the French have not taken it seriously enough because there have been so few casualties and they have been able to turn a blind eye,” said Tim Loughton, Tory MP for East Worthing and Shoreham and a member of the home affairs committee.
“The consequences tragically are that 20 or more migrants have lost their lives in French waters and those migrants could have been stopped from getting in the water in the first place.”
Tony Smith, the former director general of the Border Force, said: “I am so angry. I have told everybody that people are going to drown. This is not about immigration; it’s about people dying and we are letting them die.
“These are vulnerable people in danger. [But] the French don’t take that view. They are not saving lives. They are basically allowing unsafe boats to sail off into territorial waters which is their responsibility. For me, it is squarely on the shoulders of the French.”
Telegraph Media Group Limited