LONDON (AP) _ The government has doubled the fine for airlines that bring illegal immigrants to Britain.

Under a new law that took effect on Thursday, airlines and shipping companies bringing people into the country without valid passports or visas will be fined $3,400.

Immigration Minister Peter Lloyd said the government wants to stem the flow of people arriving without proper documents. Their numbers have doubled since 1988 to 12,000 a year, he said.

''Some carriers have made determined and successful efforts to identify these passengers before boarding, but others have not,'' Lloyd said in a statement. ''The increased charges should encourage all carriers to make stringent checks.''

Since the fines were introduced in 1987, they have been levied in the cases of 30,000 people trying to enter Britain illegally, said the Home Office, which is responsible for immigration.