Safety experts have warned that ash from an erupting Icelandic volcano that closed the country's airspace may blow across large swathes of western Europe, raising fears of new flight chaos.
Air safety officials said ash from the Grimsvotn eruption may reach north Scotland by Tuesday before sweeping across Britain to hit France and Spain two days later, as experts said the impact should not be as far-reaching as 2010 when a similar event caused widespread flight cancellations.
Ash deposits were sprinkled over the capital Reykjavik on Sunday, some 400 kilometres to the west of the volcano which spewed a cloud about 20 kilometres into the sky.
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Residents living near to Grimsvotn said the skies had turned black in an eerie echo of last year's eruption of the smaller Eyjafjoell volcano which led to the biggest global airspace shutdown since World War II.
"It's just black outside, and you can hardly tell it is supposed to be bright daylight," Bjorgvin Hardarsson, a farmer at Hunbakkar Farm in the nearby village of Kirkjubaejarklaustur said by phone.
"It's been very dark. You'd think it was night," agreed Vilhelm Tunnarsson, a photographer for local Icelandic media staying at a nearby hotel, adding at times he had been unable to see 30 centimetres in front of him.
At the moment if the volcano continues to erupt to the same level it has been, and is now, the UK could be at risk of seeing volcanic ash later this week," said Helen Chivers, Met Office spokeswoman. "Quite when and how much we can't really define at the moment."
Chivers said the weather situation is set to be different to last year, with the wind direction set to change continuously.
She added: "If it moves in the way that we're currently looking, with the eruption continuing the way it is, then if the UK is at risk later this week, then France and Spain could be as well."
While the ash has grounded aircraft in Iceland, it is not anticipated that it will have a similar impact in the rest of Europe.
Dr Dave McGarvie, volcanologist at the Open University, said that the amount of ash reaching the UK "is likely to be less than in the 2010 Eyjafjallajökull eruption", and said the last two times Grimsvotn erupted it did not affect UK air travel.
"In addition, the experience gained from the 2010 eruption, especially by the Met Office, the airline industry, and the engine manufacturers, should mean less disruption to travellers."
The April eruption of the Eyjafjallajökull volcano, in south-east Iceland, caused the worst disruption to international air travel since 9/11. Flights across Europe were cancelled for six-days stranding tens of thousands of people and was estimated to have cost airlines £130m a day.
Eurocontrol, the Europe-wide air traffic control network, said in a statement: "There is currently no impact on European or transatlantic flights and the situation is expected to remain so for the next 24 hours. Aircraft operators are constantly being kept informed of the evolving situation.