Nearly 300 flights have been scrapped and at least 28,000 bags unexpectedly separated from passengers since Terminal 5 opened last Thursday.
Jim Fitzpatrick, Britain's aviation minister, told lawmakers Monday that it could be a week before a backlog of suitcases and bags are returned to their owners.
The chaos has been a major embarrassment for British Airways and airport operator BAA PLC, which had hoped the $8.6-billion terminal would exorcise giant Heathrow's reputation as a grubby and overcrowded transport hub.
Fitzpatrick acknowledged the opening had failed to end the so-called "Heathrow hassle" for travelers passing through Europe's busiest airport.
"We had no reason to believe that the plans for T-5 would not work," Fitzpatrick told lawmakers. "It is a matter of considerable disappointment; it has dented national pride."
Theresa Villiers, transport spokeswoman for the main opposition Conservatives, said customers had been badly let down
. "Yet again, the state of Heathrow is a national embarrassment," she said.
British Airways, the only airline to fly from Terminal 5, said the terminal was working at 87% capacity Monday and service was returning to normal. But it warned there would be more cancellations Tuesday.
"It's really not ideal as an image of Britain," said Scott Basolo, waiting at the terminal to catch a flight to Los Angeles. "The folks I spoke to were just horrified that it had been such a disaster."
Heathrow's new problems come as U.S. carriers add service to London under the "open skies" treaty that took effect this month. On Sunday, Delta Air Lines, Continental Airlines and Northwest Airlines began new flights into Heathrow, and today Air France-KLM Group will fly from London to Los Angeles
The European Union-U.S. accord ends a lock on flights between the U.S. and Heathrow for British Airway, Virgin Atlantic Airways, United Air Lines and American Airlines under a 1977 agreement. The airport is attractive to other carriers as the continent's key hub for premium travel.