Hundreds of flights in and out of Britain were cancelled or delayed and the tightening of security, in response to suggestions that the alleged plotters were planning to smuggle explosives on to aircraft in fizzy drinks, involved mothers having to taste baby milk in front of guards to prove it did not contain liquid explosives. All drinks were confiscated before passengers boarded, and only the barest of essentials were allowed to be carried as hand luggage, and in clear plastic bags.

Stephen Nelson, chief executive of the airport operator BAA, said that airports had never “faced a security mandate of this scale and severity”. Douglas Alexander, the Transport Secretary, said that authorities had had “no choice” but to impose the stricter rules and urged passengers to “show understanding in the inevitably difficult circumstances”.

Despite the huge disruption, all seven BAA airports remained open for business.

Last night, flight schedules at most of the country’s airports began returning back to normal, with most arrivals and departures back on schedule.

The ban on short-haul flights into Heathrow was lifted and by yesterday evening, about half of all flights were departing or arriving. Delayed flights were taking off and landing through the night to clear the backlog.

Flights at Luton, Stansted and Gatwick were expected to return to normal today with aircraft last night taking off at both airports as scheduled, although some delays may still occur, and stringent security measures remain in place.

At Manchester airport, flights were operating with delays of between 40 and 90 minutes.

Yesterday morning, there had been confusion among passengers over the tightened security, with those who arrived for early flights gleaning more information from calls to relatives watching television at home than from staff on the ground. Eventually airport staff grasped the situation began to explain the rules. Passengers who managed to check in had to pack away their mobile phones.

More than 185,000 people were yesterday due to pass through Heathrow. The world’s busiest airport became a mêlée of desperate holidaymakers, businessmen and crying children, with airport staff milling around trying to establish control.

Mountains of luggage piled up as passengers tried to repack their bags in accordance with the new security rules, keeping only the bare essentials in plastic bags, and lengthy queues snaked round the terminal buildings.

By early afternoon the airport announced that all short-haul and domestic flights had been cancelled and that there would be lengthy delays for long-haul passengers. Airlines made repeated requests for those booked on cancelled flights to leave the airport but it took hours for the crowds to thin. Some who had checked in bags on to grounded flights were left without even the keys for their car and house.

Passengers queued patiently for payphones, internet cafés, cash points, luggage shops, lavatories and restaurants. But the biggest wait was for the airport information desks. Dozens of staff patrolled the queues, trying to reassure their customers but imparting little information.

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