Lone children were held at UK-run detention centres in France on nearly 300 occasions last year, according to documents released under the Freedom of Information Act. Data obtained by the Guardian shows they are part of about 900 instances when unaccompanied minors have been detained at British short-term facilities near Calais and Dunkirk over the last four years. Refugee charities said the numbers were “shocking” and raised concerns about secrecy surrounding the treatment of children held in UK-run facilities in France. Inspectors last year described “poor” conditions at the sites, while NGOs have said they are “legal and procedural grey zones”. The short-term holding facilities – Coquelles freight, Coquelles tourist, Calais tourist and Dunkirk – are designed to hold clandestine travellers and those suspected of having incorrect paperwork for no longer than 24 hours. Despite being run by the UK government, data on who is held by the UK in France is not published as part of official immigration statistics.…