Air travellers were assured that the security measures causing delays and cancellations were "time-limited" as airlines and Britain's largest airport operator squabbled over who was to blame for the misery.
The Home Secretary, John Reid, admitted that the checks at airports were not "indefinitely sustainable" as thousands of travellers endured a fourth day of disruption. And late last night, the government announced the security threat at UK airports had been downgraded from "critical" to "severe".
The downgrade will mean passengers will be able to carry one item of hand luggage for most flights, but would still be banned from carrying liquid onto flights.
The decision is likely to be met with relief by both passengers and the travel industry. Throughout yesterday, Heathrow, the world's busiest international airport, continued to be the worst affected by the tightened security with a third of flights cancelled and travellers facing long delays.
But amid frustration for some 12,000 travellers at London's airports yesterday, Mr Reid appeared to offer hope of a relaxation of the measures. He told BBC News 24: "We have always imagined that the present regime is time-limited. We know it is not indefinitely sustainable and we're trying to get a regime that is capable of protecting the public, but allows maximum movement for airlines, operators and passengers."
Airlines and airport operators accepted that tougher restrictions were necessary at a meeting with ministers on Friday but, following the chaotic weekend scenes at Heathrow and other airports, a fresh round of talks is expected today.
Officials were expected to work through the night to draw up new proposals to be put to airlines and airport operators. The British Airports Authority (BAA), which runs Heathrow, Gatwick and Stansted airports, said the emergency measures banning hand luggage and requiring the body search of all passengers were "not sustainable". The company said there would be a similar but "slightly reduced" level of cancellations today.
Amid open criticism of BAA by British Airways, the continuing chaos at airports brought calls from the Conservative Party for troops to be brought in to assist with the searches.
David Davis, the shadow Home Secretary, said: "BAA is clearly not set up for this level of scrutiny and it does seem to me there is an argument for some resources being put in there, and put in there quickly to try to rescue as many holidays as we possibly can."
The measures, introduced by the Government following the arrests relating to an alleged plot to blow up transatlantic aircraft, allow passengers to carry only essential items on to flights and require all travellers to be body-searched rather than a previous rate of one in every four.
In a sign that the tension between airlines, operating to tight schedules, and the airport operator has reached breaking point, Willie Walsh, the BA chief executive, bluntly accused BAA of failing to cope. The airline said it had cancelled 30 per cent of its flights from Heathrow yesterday and all its domestic flights to and from Gatwick. Mr Walsh said: "The Heathrow baggage system cannot process all of the passengers' bags and where passengers have been able to check in their bags, the queues in the airport search area means that passengers are unable to get to the departure gate in time for their flight."
BAA blamed the measures themselves and said the level of cancellations and delays was the price to be paid for enforcing them. Tony Douglas, in charge of Heathrow for BAA, said: "If this is maintained, we are likely to continue to see extremely long queues and, regrettably, even more flights cancelled. I don't know how long it's likely to go on, but it's clearly a set of measures that are unprecedented and, by virtue of what they've come in to enforce, they're not sustainable measures."
Anger was also focused on the Department for Transport prior to its announcement last night. Michael O'Leary, the chief executive of Ryanair, which relies on fast turnaround times to maintain its profit margins, suggested the disruption was allowing terrorists to "achieve many of their objectives" by disrupting the economic life of Britain. The Irish airline said it had had to cancel 20 per cent of its flights out of Stansted yesterday to accomodate the new security measures. He called for a reduction in passenger searches.