The government of Charles de Gaulle held hundreds of foreigners, including at least three Britons, in an internment camp near Toulouse for up to four years after the second world war, according to secret documents.

The papers, part of a cache of 12,000 photocopied illegally by an Austrian-born Jew, reveal the extent to which French officials collaborated with their fleeing Nazi occupiers even as their country was being liberated. They also show that, when the war was over, France went to extraordinary lengths to hide as much evidence of that collaboration as possible.

The documents are in a mass of registers, telegrams and manifests which Kurt Werner Schaechter, an 84-year-old retired businessman, copied from the Toulouse office of France's national archives in 1991. They are uniquely precious: under a 1979 law most of France's wartime archives are sealed for between 60 and 150 years after they were written.

"This is an untold story of the dark side of France's liberation 60 years ago," Mr Schaechter, a former musical instruments salesman, said at his home in Alfortville, a Paris suburb."French functionaries were involved in a national scandal that continued until 1949: the despicable treatment of allied and neutral civilians interned during the war."

Mr Schaechter's activities - last year he used some of the papers to try to force the French railway SNCF to admit its responsibility in shipping 76,000 Jews to Nazi death camps - have infuriated some French historians, who say their privileged access to classified archives has been compromised. But others have backed the campaign for freer access to documents relating to a part of France's past that it has long preferred to ignore.

By far the most awkward of his recently unearthed documents are those that appear to show that Noe camp, 25 miles south of Toulouse, continued to function secretly for several years after the war. Noe was one of 300 camps set up after 1939 to hold Jews, communists and other"anti-French" militants, Gypsies, common criminals and enemy aliens.

Many of its inmates were quickly shipped out as France was progressively liberated in the summer of 1944. But, said Mr Schaechter, not everyone could be got out in time:"Allied bombing of the railway lines, and intensified fighting on the ground, meant many simply could not be moved."

Officially, the only camps still open after 1945 were a handful housing Romanies, stateless persons and French collaborators. But Mr Schaechter says his documents indicate that a"special section" of Noe was active until at least 1947.