A 16-year-old British schoolgirl has been left stranded in Denmark after she was not allowed to board a flight to London because of new UK border rules introduced on British dual nationals.Hanne*, from Sussex, was stopped from boarding a flight home on 8 March after a weekend seeing her British father, who is an academic on a short work stint at a university in Copenhagen.She had travelled with her Norwegian-born mother but was still waiting for a British passport, which she had applied for before the trip.Her Liberal Democrat MP, James MacCleary, called on Keir Starmer and Shabana Mahmood to intervene, saying a school child now faced “a nail-biting wait” overseas “due to the government’s mishandling of this situation”.Like hundreds of others known to the Guardian, her parents did not know of the rule change brought in by the Home Office.Hanne, who is sitting her GCSEs in May, has now missed two weeks of school and is facing a potential six-week wait for a passport. The first the family knew about the new border rules was when they tried to check in for their return flights. “We tried to check in on the app and it allowed me to check in but not Hanne,” said her mother, Ingrid*. “When we got to the airport and they wouldn’t let her check in either.”The airline, Norwegian, rang the British embassy in Copenhagen but they could not help. One immigration lawyer said the Home Office could be breaching laws concerning the welfare of children.“Obviously it is very stressful,” Ingrid added. “We are very worried about the GCSEs, she is missing school, missing her mother, her siblings and all the other things in her life.”“It will be a disaster if she can’t come back soon.”MacCleary said: “The Government’s hopeless planning and communication of its changes to entry requirements for dual nationals has caused an untold amount of chaos and stress.