The 16-year-old Sudanese boy was trying to reach the UK in a small boat when it capsized in the early hours of Wednesday morning.
His friend, also thought to be a Sudanese teenager, made it to shore and alerted authorities but the boy’s body was later found on Sangatte beach.
Pierre-Henri Dumont, who represents Calais in the French National Assembly, wrote on Twitter: “What we all feared happened that night.
“How many more tragedies will it take for the British to regain an ounce of humanity?
“The inability to apply for asylum in Britain without being physically present is causing these tragedies.”
Mr Dumont said that migrants living in informal camps around Calais, despite a series of forced evictions in recent years, did not want asylum in France and had refused state support.
He warned that the number of people living in camps and attempting crossings had been rising, adding: “Britain’s carelessness does not exonerate the French government from its own responsibility.”
Priti Patel called the boy’s death an “upsetting and tragic loss of a young life” as talks continue with France aiming to stop small boats leaving its coastline.
The home secretary added: “This horrendous incident serves as a brutal reminder of the abhorrent criminal gangs and people smugglers who exploit vulnerable people.”
But local reports suggested that smugglers were not involved in the crossing attempted by the boy who drowned.
An official from the Boulogne-sur-Mer prosecutor's office, which is investigating the death, told the Nord Littoral newspaper the boy and his friend stole an inflatable boat from a chalet in Sangatte, along with shovels to use as oars.
The vessel was a small dinghy that can be purchased in supermarkets, officials said, and inflated by mouth.
Experts believe that the wake of a passing ferry or commercial ship would have been capable of overturning it.
The friend of the boy who died, who was suffering from hypothermia, alerted authorities shortly after 1am on Wednesday.
“[He said] that they capsized and his companion must still be in the water,” said a statement from the maritime prefecture for the Channel. “He also warned that his companion could not swim.”
A sea search was carried out using boats and a Belgian air force helicopter, but was called off at around 4.30am when nothing was found.
Authorities were alerted to the discovery of the boy’s body at 8am.
It came weeks after the Home Office announced a new “joint action plan” with France and put a former Royal Marine in the post of “clandestine Channel threat commander”.
The RAF has sent surveillance aircraft to assist the Border Force, after the UK gave France millions of pounds to increase security along its coastline.
Children were among more than 50 migrants who arrived in Dover on Wednesday morning, bringing the total number for this year to more than 4,700.
Anne McLaughlin, co-chair of the All-Party Parliamentary Group on Refugees, said the boy “took the risk because it was his only chance”.
“We can only imagine what his final moments were like,” she told The Independent. “When it comes to these terrifying situations, the entire focus of the home secretary must be on creating safe routes for people to exercise what is, after all, their legal right to apply for refuge.”
The shadow home secretary, Nick Thomas-Symonds MP, said the government's response to rising Channel crossings had been “lacking in compassion and competence”.
“Ministers urgently need to step up work with international partners to find a humanitarian solution to this crisis, which is costing lives,” he added.
Humanitarian group Detention Action called on the home secretary to resign.
The boy is one of several migrants to have died while attempting to reach the UK in recent years.
United Nations figures show that more than 19,500 migrants have lost their lives attempting to reach Europe across the Mediterranean Sea since 2014, but the death toll for the English Channel is not formally recorded.
Last week, the UN Refugee Agency (UNHCR) called for the British and French governments to make saving lives the “first priority”.
A parliamentary report released in November also called for the UK government to increase search and rescue operations and found its own policies were “pushing migrants to take more dangerous routes”.
A Home Office spokesperson said: “The UK has a long and proud history welcoming those in need and escaping persecution and resettles more refugees than any other country in Europe.
“There are safe routes to claiming asylum for those in need and since 2015, we have resettled more than 25,000 refugees, around half of whom were children.”
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