Mainlanders arrested while attempting to claim right of abode have a valid legal basis for fighting attempts to remove them, lawyers said yesterday. But some experts suggest they should not start legal proceedings until after the Government announces new procedures for obtaining certificates of entitlement on the mainland. One lawyer said: 'I don't think there is any doubt they have an arguable case. Whether it is in their best interests to argue it is another matter.' Migrants arrested yesterday may be able to claim that the landmark Court of Final Appeal ruling two weeks ago makes it unlawful for them to be removed. The court said the Government was entitled to establish a reasonable scheme for migrants to obtain certificates of entitlement on the mainland. But such a scheme is not yet in place. It would be two or three weeks before new procedures were announced, an Immigration Department spokeswoman said yesterday. 'Two-way permit holders are supposed to come to Hong Kong to visit or for sight-seeing,' she said. 'But if they overstay, according to Hong Kong law, we have to remove them.' Lawyers say that if new test cases are launched, the migrants are likely to argue it is unlawful to send them back to the mainland to comply with procedures that do not yet exist. One said: 'There is a body of argument to the effect that at least now, while there are no procedures for applying in the mainland . . . it would be unreasonable to remove them, because they can't apply there.' The migrants can seek legal aid and lodge an application for permission to proceed with a judicial review at the High Court. It is thought they would have a good chance of securing permission to proceed to a full court challenge on the basis that they have a strong enough case to be argued before a judge. If a hearing was ordered, it is likely the migrants would be allowed to stay in Hong Kong until it was decided. The last case took 18 months to reach a conclusion at the Court of Final Appeal. For this reason some lawyers are suggesting the migrants may be better off postponing court action until the Government announces the procedures. The future scheme may enable them to obtain certificates on the mainland and return to Hong Kong as permanent residents much quicker than could be achieved by going to court.