Many of the people living in The Jungle in Calais are probably not refugees "in any general sense", Britain's most senior immigration judge has said.
They are more likely to be migrants who decline to make a claim for asylum in France because of the "perceived advantages" of lodging an application in Britain, Mr Justice McCloskey suggested.
It came as the President of the Upper Tribunal Immigration and Asylum Chamber set out the reasons for a l andmark legal ruling allowing four Syrian refugees to come to Britain from the sprawling camp last week.
Lawyers for the young men - three teenagers and a 26-year-old with mental health problems - argued that they faced "intolerable" conditions and had a right under Article 8 of the Human Rights Act to be reunited with family members already living in Britain legally.
Judges agreed that the four should be brought across the Channel while their asylum claims are determined, and they arrived last week in London.
Under European rules known as the Dublin Regulation, asylum seekers must make a claim in the first country they reach but can have their application examined in another country if they have relatives there.
Once an application is lodged in France, the process for formally passing it to the UK can take up to a year. The tribunal's ruling meant the four Syrians could be admitted to the UK as soon as their claim was lodged in France rather than waiting there while it passes through the French system.
The full ruling handed down on Friday said: "It seems likely that there is no real basis for many of its occupants remaining indefinitely in The Jungle and enduring the conditions that obtain there.
"Many are probably not refugees in any general sense or any sense entitled to recognition.
"Rather, they are migrant nationals of a number of countries outside the European Union, who, while intending to make a claim for refugee status, decline to make the claim in France due to perceived advantages, correct or otherwise, of doing so in the United Kingdom.
"In general terms there is no basis at all for thinking that a person who claims asylum in France will not be treated properly and will not have the benefit of the reception and other facilities which those duties entail."
However, it said the four were in a "special, indeed unique situation" because of factors including their age, vulnerability, psychologically traumatised conditions, the "acute and ever present dangers" to which they are exposed in The Jungle, the mental disability of one applicant, the "claimed" relationships linking them to those already in the UK and the "firm likelihood" that the outcome of applications in France would be a "take charge" acceptance by the UK.
The ruling described The Jungle, where an estimated 6,000 people are gathered, as a "bleak and desolate" place, adding: "Unlike other jungles, this place is inhabited by human beings, not animals. The conditions prevailing in this desolate part of the earth are about as deplorable as any citizen of the developed nations could imagine."
The judgment found the refusal to permit "swift admission" for the four "would interfere disproportionately with the right to respect to family life".
It went on: "Our conclusion is that the balance tips in favour of the applicants provided that they are prepared to set in motion their asylum claims processes in France."
However, the ruling stressed judges "will not lightly find" that Article 8 "operates in a manner which permits circumvention" of the Dublin Regulation, adding: "We consider that such cases are likely to be rare."
George Gabriel, of the charity Citizens UK, said they expect the judgment to affect 200 or 300 young people and unaccompanied minors in Calais and Dunkirk.
He added: "We hope to roll out legal support for them in a matter of days."
Steve Symonds, of Amnesty International UK, said: " For the UK Government to fight this case all the way to court is a demoralising reminder of how it continues to shirk its responsibility to provide safe refuge to those already forced to flee to Europe."
A Home Office spokesman said: "We have been granted leave to appeal and will be challenging the Upper Tribunal's judgment ."