Intelligence agents study cache of leaked Isis documents

British, US and German intelligence agencies are looking for potential leads in thousands of documents purporting to list Islamic State volunteers, while admitting that much of the information has been overtaken by events and that many of those named are dead.

Many of the 14 Britons whose details appear in the documents, copies of which were provided to the Guardian by the German newspaper Süddeutsche Zeitung, had already been identified publicly as fighting for Isis and most appear to have been killed.

The documents are questionnaires for would-be Isis recruits, listing their real names, their fake names, who introduced them, their countries, experience of jihad, education, date and place of birth, date of arrival in Syria, route, phone number and family.

Some analysts on Thursday cast doubt on the authenticity of the documents, pointing out mistakes and uncharacteristic language, although both British and German intelligence agencies indicated they had no reason to believe they were fake.