Lorna Gordon reports from Iceland on coastguard footage from 19 April
A new ash cloud spreading towards the UK is causing uncertainty over plans to reopen some airspace on Tuesday, air traffic control body Nats has said.
Earlier, it said the flight ban would be lifted over Scotland, Northern Ireland and the north of England.
But Nats said there was now a worsening situation in some areas. The outlook for Northern Ireland is most uncertain.
Glasgow Airport and Newcastle International Airport said they were to reopen for certain flights at 0700 BST.
Flights from Newcastle are expected to head to Aberdeen and the Isle of Man.
And the first flights out of Glasgow are going to Stornoway and Islay, while the first international flight is expected to depart at midday going to Reykjavik, in Iceland.
Nats, which is due to report again at 0900 BST, has said more airspace over England was expected to become available from 1300 BST, although not as far south as London's main airports.
In a statement it said: "The volcano eruption in Iceland has strengthened and a new ash cloud is spreading south and east towards the UK.
"This demonstrates the dynamic and rapidly changing conditions in which we are working."
While some airports in Scotland and the north of England said they expected flights to be leaving during the morning, a spokesman for Belfast City Airport in Northern Ireland said: "Bar the activity to the Isle of Man, we expect to have nothing before lunch-time."
British Airways has cancelled all short-haul flights on Tuesday but said it hoped to run long-haul flights scheduled to depart after 1600 BST depending on a "full and permanent" opening of airspace.
Manchester Airport said it was sticking to plans to open at 0900 BST on Tuesday, but would monitor Nats reports.
EasyJet flights to and from Northern Europe, including the UK, have been cancelled until 1800 BST on Tuesday.
Nats said it expected the situation to change during the course of the day, and emphasised it was in regular contact with the Met Office and the UK's safety regulator, the Civil Aviation Authority.
It added: "We are working closely with government, airports and airlines, and airframe and aero engine manufacturers to get a better understanding of the effects of the ash cloud and to seek solutions."
There have been calls from the industry to review the flight restrictions - said to be costing airlines $200m (£130m) a day - after a number of test flights showed no obvious damage to aircraft.
BA said it was among European carriers that had asked the EU and national governments for financial compensation for the closure of airspace.
The British Air Transport Association has also written to Transport Secretary Lord Adonis asking the government "to commit to standing behind the industry financially at this very difficult time".
UK traveller: "We drove 2150km in two days"
In a statement released shortly before Nats', the Met Office said: "Eruptions from the Eyjafjallajoekull volcano are weaker than they were at the weekend but eruptions still take ash over 10,000ft at times.
"Weather patterns continue to blow areas of ash towards the UK.
"As the volcanic activity changes, there may be some clearance of ash at times, over parts of the UK."
The spread of volcanic ash has affected large swathes of Europe for the past five days. The event has caused huge disruption for air travellers, many of whom have embarked on long and costly journeys over land and sea to get home.
Some have then been further hit by rail strikes in France.
Prime Minister Gordon Brown said three Royal Navy ships had been earmarked to help bring home some of the estimated 150,000 Britons stranded abroad.
Hundreds of British soldiers from 3rd Battalion, The Rifles are being airlifted by chartered civilian jets from Cyprus to Spain, before sailing to the UK aboard HMS Albion.
The ship, which arrived in the Spanish port of Santander on Tuesday morning, may also carry civilians on its return.
The other two ships, HMS Ark Royal and HMS Ocean, are to go to the English Channel.
The UK government's emergency committee, Cobra, met twice on Monday and plans to meet again on Tuesday.
After the second meeting a No 10 spokesman said the committee agreed the government should "continue to do whatever it can" to return stranded Britons to the UK.
The EU has now moved to ease air travel curbs with transport ministers saying there would be a core no-fly area, an open-skies area and a third limited-service zone.
Some flights have now taken off from Amsterdam.
Planes were first grounded in the UK at midday on Thursday amid fears particles in the ash cloud from the Eyjafjallajoekull volcano could cause engines to shut down.
Air travellers, due to fly into reopened airspace, are being advised to check the status of their flight before travelling to the airport.
Celebrations on a brand new £500m cruise ship have been put on hold to rescue about 2,000 British tourists stranded in Spain. Luxury vessel Celebrity Eclipse is due to leave Southampton for Bilbao on Wednesday evening, returning on Friday
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