Under the Single European Act, which came into force in January 1993, all people in the European Union should be allowed to move freely between member countries.
But the British Government in 1985 inserted a clause into the act, allowing it to impose checks for controlling immigration from third countries, and to combat terrorism, crime, drug trafficking and illicit trading in works of art and antiques.
Immigration campaigners say this clause has no force in law, and members of the Conservative Party, fearing the campaigners are right, claim the Single European Act will allow millions of immigrants into the UK.
The 16 UK residents in tomorrow's test case are members of an organisation called the Standing Conference on Racial Equality in Europe (SCORE). Last year on a day trip to France they complied with three separate passport checks at Dover at the start of their journey.
But on their return, they refused to show their passports, arguing that immigration controls on visitors from other member states breach the Treaty of Rome.
They were detained and released only after the operators of Hovercraft that brought them back from France assured immigration officials that all passengers had carried passports.
Tomorrow the group will ask for the case to be referred to the European Court of Justice.
The government is likely to contest the case fiercely.Reuse content