The European Court of Justice is being asked to rule on a test case which might allow millions of Hong Kong people greater access to Britain and other EU countries. The court is to consider whether British National (Overseas) passport holders have an automatic right to remain in European Union nations because they hold a British travel document. London-based immigration lawyer David Tang Hon-sing said up to 3.5 million Hong Kong people could be affected by the ruling. 'This case is very important for Hong Kong people because it would give them the right to remain in Britain and would mean they could not be deported,' Mr Tang said. He said he was dealing with about a dozen cases involving people from the SAR who had been told they could not remain in Britain. 'While we are waiting for this case to come before the European Court of Justice, all these people have the right to stay in Britain,' Mr Tang said. 'I have one case involving two sisters who came here on holiday to join their mother who is a British citizen. 'They were refused the right to remain and told they would have to go back to Hong Kong, but now they have been allowed to stay pending the outcome of the case.' The test case before the court involves an Indian woman who was born in Kenya and holds a British National (Overseas) passport, similar to those issued in Hong Kong before the handover. She was refused permission to remain in Britain, but in December the High Court decided to refer her case to the European Court of Justice. It has been submitted that British National (Overseas) passport holders also have the right to live freely in the European Union. Cases usually take between 18 months and two years to come before the European court. Until the case is decided, the passport holders concerned cannot be removed from Britain. 'I'm not telling Hong Kong people to pack up and come over here but if they are in the UK and want to remain in the UK they at least have the right to stay until the court makes a decision,' Mr Tang said. Juan Victor Monfort, a counsellor at the European Union Office in Hong Kong, said he expected the court to decide whether British legislation conformed with the Maastricht Treaty and the Treaty of Rome. The Maastricht Treaty says citizens of any European Union member country can move freely and stay in other member states. Rights of citizenship and free access are decided by individual states.