Airlines rushed to reschedule flights but there were warnings it could be weeks before services return to normal.

The Civil Aviation Authority (CAA) stepped in to ease restrictions on Tuesday night and described the chaos as a "a situation without precedent".

It is estimated hundreds of thousands of passengers were left stranded abroad in a shutdown thought to have cost the industry about £130 million a day.

Willie Walsh, chief executive of British Airways, said "lessons can be learned" from the handling of the event and added: "I don't believe it was necessary to impose a blanket ban on all UK airspace last Thursday.

Air traffic control company Nats insisted it faced no political pressure to ease the restrictions.

"We don't feel we have been under pressure from the Government," said spokesman Alex Bristol. "Where the pressure has come has been to better understand the safety implications."

A spokesman for BAA, which operates airports including Heathrow, said it would do everything possible to "get people moving".

"We are ready to open, but until further notice passengers must contact their airline before travelling to the airport," the spokesman said.

"Not all flights will operate during the early period of opening, and we will do everything we can to support airlines and get people moving."