BRUSSELS  Northern Rock may be getting government aid for longer than necessary, according to an official European Commission document that suggests that the nationalization of the troubled British lender faces tough scrutiny from regulators.

Opening an inquiry into whether the bailout broke European Union rules on state aid, the commission listed a series of reservations about the deal that shored up the mortgage lender.

Northern Rock was the worst victim in Britain of the tight credit market, which was set off by the subprime mortgage crisis that began in the United States last year. After an unsuccessful search for a buyer for Northern Rock, the British government nationalized the bank in February.

Earlier this week, another big British mortgage lender, Bradford & Bingley, had to seek emergency help from investors and cut the price of a planned share sale.