Around 150,000 still marooned abroad as pressure mounts on airlines to restore schedules after flight ban is lifted

The lockdown of British airports came to an end last night as the no-fly order was lifted and airlines began the task of bringing home tens of thousands of stranded passengers.

Airports are expected to remain open after test flights and new analysis of the ash cloud established it was safer to fly than had been believed but it will be several days and perhaps more than a week before the last of the 150,000 Britons stranded abroad are able to get home.

The National Air Traffic Service welcomed the move and said just a small area of airspace over north-west Scotland remained out of bounds to aircraft because of the concentration of ash. "This brings to an end a period of disruption and uncertainty for air passengers," it said in a statement.

A spokeswoman for BAA warned there were likely to be delays and cancelations before normal levels of service can be resumed. She said: "Until further notice passengers must contact their airline before travelling to the airport. Not all flights will operate during the early period of opening.

In the first stage of a state-run rescue mission, the warship HMS Albion was returning from Spain carrying 300 stranded Britons and 400 troops. But the Government admitted there was not likely to be a large-scale seaborne rescue – plans to use the aircraft carrier HMS Ark Royal and the commando helicopter carrier HMS Ocean have not been finalised.

The airline and travel industries reacted with huge relief that the no-fly orders that crippled air travel in Britain and much of northern Europe for six days finally seemed to be at an end. There was, however, mounting anger among many industry figures who believe the no-fly orders were much too broad and should have been lifted or at least reduced much earlier.

Willie Walsh, British Airways' chief executive, was among those unhappy at the extent of the lockdown. "I don't believe it was necessary to impose a blanket ban on all UK airspace last Thursday," he said. "My personal belief is that we could have safely continued operating for a period of time."

He was convinced "lessons can be learned" from the experience but said the priority now was to bring home stranded passengers and resume normal services. "There will be plenty of time for a post-mortem of what has happened over the last few days," he said. "We are now going to start the difficult task of getting our stranded customers home. This is an airlift which has been unprecedented."

British airspace was declared open shortly before 10pm – the first flight into Heathrow, from Vancouver, landed at 9.50pm – after experimental flights and other research established that the volcanic ash cloud was less deadly to aircraft engines than it had been a week ago.

Aviation experts and volcanologists now have a clearer understanding of the concentrations of ash needed to damage aircraft engines and enabled the authorities to lift the ban on flights.

The Civil Aviation Authority (CAA) will use new guidlines to assess when and where ash clouds pose a danger to aircraft. Small no-fly zones are still in force for some parts of the ash cloud but none are in British airspace. The ash cloud was created by a volcano in Iceland but with the nature of the eruption changing and weakening it is thought unlikely to pose much more of a threat to aircraft over Britain.

Dame Deirdre Hutton, chief executive of the CAA, said last night that safety had been paramount and that it had taken time to gather evidence necessary to provide assurances that it is now safe to fly over Britain. "We had to ensure, in a situation without precedent, that decisions made were based on a thorough gathering of data and analysis by experts," she said.

"This evidence-based approach helped to validate a new standard that is now being adopted across Europe. The major barrier to resuming flight has been understanding tolerance levels of aircraft to ash. Manufacturers have now agreed increased tolerance levels in low ash-density areas. Our way forward is based on international data and evidence from previous volcanic ash incidents, new data collected from test flights and additional analysis from manufacturers over the past few days."

Lord Adonis, the Transport Secretary, expects all the airports to remain open now there is a better understanding of the effects of ash. "Since the flight restrictions were imposed, the CAA have been working around the clock with the aircraft manufacturing industry, the airlines and the research community to better understand how different concentrations of ash affect aircraft engines," he said. "As a result, the CAA has now established a wider area in which it is safe to fly, consistent with the framework agreed by the EU transport ministers yesterday."

Until the announcement last night, only a few flights could take advantage of a short break in the volcanic ash cloud in Scotland yesterday before more debris from Iceland wrecked hopes of reopening all airports during the day. Theresa Villiers, the shadow Transport Secretary, said: "This is welcome news and will come as huge relief for many but we must not forget the hundreds of thousands stranded abroad. The Government must still prove they have a clear and properly thought-through rescue plan to deal with the massive backlog."

As part of the rescue operation, five coaches carrying 250 Britons were due to leave Madrid last night after the British Embassy there managed to arrange transport.