Sunday's flight BA223, scheduled to depart at 1505 GMT, took off from Heathrow Airport just after 1815 GMT. Armed police stood guard at the departure gate, and the 241 passengers were quizzed by detectives before being allowed to board the 747-400 jumbo jet.
"What I can say is that I fear that for many years to come we're going to be living in an age where there is a heightened state of alert," Transport Secretary Alistair Darling told British Broadcasting Corp. television.
"Sometimes it will be quite severe, at other times perhaps less so, but it does mean that we're going to have to get used to increased security at airports," Darling said.
Hundreds of passengers were stranded when British Airways canceled flight 223 from Heathrow to Washington's Dulles airport on Thursday and Friday on government advice. Neither the airline nor British officials would provide details of the threat, although analysts and media reports suggested authorities had received intelligence of a possible airborne attack by al Qaeda linked terrorists.
Flight 223 was allowed to take off Saturday, but was delayed for more than three hours by thorough security screening.
CBS News Correspondent Joie Chen reports Saturday's flight 223 only carried half it's typical passenger load, raising the questions: How many more flights can the airlines afford to cancel? How long can this level of scrutiny and security go on?
Even as they demonstrated stepped up security at their airports, foreign governments expressed frustration with U.S. demands for greater scrutiny of their flights.
Terrorism expert Paul Beaver tells Chen, "We've got to the stage in Western Europe where nobody actually takes any notice of American alerts anymore because there's so many of them."
BA spokesman Paul Parry said the delays Saturday and Sunday were due to a U.S. request for extra security information.
"They have requested to be supplied with extra information about the flight for security purposes before take-off to Washington, the same as happened yesterday," he said.
In response to U.S. security demands, the European Union agreed last month to share airline passenger lists for all U.S.-bound flights with American officials. U.S. officials also have sought to get armed "sky marshals" deployed on some flights.
A dozen flights to and from the United States have been canceled in the two weeks since the Bush administration raised the national terrorism alert to orange, its second-highest level, saying there was intelligence terrorists could be planning large-scale attacks over the holiday season.
Darling declined to comment Sunday on media reports that the British government had received intelligence that al Qaeda was planning to use British Airways flights to launch suicide attacks on prominent targets in the United States.
But he said the decision to cancel the flights, as well as one Saturday to the Saudi Arabian capital, Riyadh, were justified on the basis of intelligence warnings. And he warned travelers to expect an increased number of airline security alerts in the coming years.
"We are going to have to get used to increased security at airports," Darling told the BBC's "Breakfast with Frost" program. "From time to time that will be noticeable and at other times maybe things will be going on behind the scenes."
Prime Minister Tony Blair also said some delays were inevitable.
"You know the terrorist threat is real right around the world at the present time. Nobody is immune from it, you have to remain vigilant," Blair told reporters as he flew back from a brief visit to British troops in Iraq.
"People should have faith with the authorities, the airlines and all of us. We are doing the very best with the situation we have," Blair was quoted as saying by Britain's Press Association news agency. "In general terms, the terrorist threat is there, there's no point denying that. It was there before Sept. 11."
British Airways said it had not yet decided whether Monday's scheduled flight to Riyadh would go ahead.