Children in the Calais "Jungle" are risking their lives every night as they attempt to reach the UK, Britain's anti-slavery commissioner has warned as he called for ministers to step up efforts to address the plight of lone youngsters in the camp.
Minors are turning to smuggling gangs amid frustration at official routes for claiming asylum or joining relatives who are already in this country, Kevin Hyland suggested.
In a letter to Home Secretary Amber Rudd, he painted a stark picture of the threats faced by children and other vulnerable individuals living in migrant camps such as the Jungle.
In a conclusion that will heap fresh pressure on the Government over the issue, he said he is convinced that frustration with, and lack of confidence in, regulations known as the Dublin III procedures "is one of the key motivators behind risk taking behaviour, which leads to higher exposure to modern slavery and exploitation".
Under Dublin III, asylum claims must be made in the first safe country a person reaches - but children can have their claim transferred to another country if they have family members living there.
Campaigners have repeatedly called for the process to be sped up so an estimated 185 children believed to be eligible for humanitarian protection in the UK can be transferred from Calais.
The issue came under fresh scrutiny at the weekend after a teenage Afghan boy - named as Raheemullah Oryakhel and said to have a legal right to travel to Britain - died as he tried to climb on to the roof of a lorry near Calais.
In his letter, Mr Hyland commended the work of the British and French governments to secure borders and tackle smuggling networks - but added that not enough is being done to "address the vulnerabilities of migrants, in particular unaccompanied children".
Mr Hyland said he received a "clear message" that there is "very little confidence in asylum seeking procedures in France", as well as the Dublin III regulations.
Some people had already applied for asylum in France or family reunification under Dublin III, but "every night they were continuously trying to cross the Channel illegally".
The letter said: "The waiting time was simply far too long for them. Unfortunately, migrants had more trust in smugglers than in state led procedures that exist to ensure their protection."
Mr Hyland recounted a story he was told of a woman with two young children who had family in the UK but was afraid to register for asylum in France.
"She viewed her only option as going to smugglers to get herself and her children to the UK," he said.
He said the Government should provide increased resources - and possibly deploy staff - to quickly identify children who qualify to be reunited with relatives in Britain, or relocated here under another initiative to bring unaccompanied refugee children from Europe.
Mr Hyland also suggested that a fast-track system should be considered.
"Children are not waiting," he wrote. "Every night they go to their smugglers who have promised to get them across the Channel. Every night they think that this time they will be lucky. However, every night each of these children are at risk of exploitation and sadly even dying as they take huge risks to reach the UK."
Statistics indicate that in August there were 865 children living in the Jungle, with 676 of that number unaccompanied.
The commissioner, who visited Calais earlier this year, described living conditions in the camp as "unsuitable and unsafe".
Groups identified by a project as being at high risk of exploitation and trafficking include young women from countries of the Horn of Africa and Egyptian boys who are forced to steal in Calais town and bring goods back to the camp, according to the letter.
A Home Office spokeswoman said:"Our priority is to offer humanitarian support to those most in need and we work closely with the French Government to protect those vulnerable to trafficking and exploitation.
"We are dedicated to ensuring that children in Calais with family links in the UK are identified, receive sufficient support and can access the Dublin family reunification process without delay.
"Over 120 cases of unaccompanied children in Europe have been accepted for transfer to the UK under the Dublin Regulation since the start of the year and we want to build on this progress.
"We will respond to the commissioner's recommendations in full, in due course."
The French Government has committed to dismantling the remainder of the Calais camp by the end of the year and relocating migrants to more suitable accommodation.
A spokeswoman for the French embassy in the UK said applications for family reunification are dealt with the same day they are lodged, and transmitted directly to the British authorities.
She said this "close cooperation" has already enabled around 70 minors to be legally reunited with members of their family in the UK, adding: "Of course, the government is closely monitoring the situation in Calais, and I am sure they will pay great attention to the observations made by Commissioner Hyland in his letter."
Unicef UK said relatives of Raheemullah Oryakhel, reportedly aged 14, had a room in their home prepared for him and said his death was the result of a "lack of action".
Lily Caprani, the charity's deputy executive director, said: "This tragedy must now lead to action. The UK must work with the French authorities to get children into appropriate accommodation, where they can have access to care and legal support so they can reach their families safely. It's in the UK Government's hands to prevent any more children from being killed."