Thousands of confused and angry passengers wandered around Britain's becalmed airports today trying in vain to find out how long the disruption caused by the ash cloud might last.
Airports across the UK came to a standstill after the air traffic control company Nats decided that the climatic conditions posed a serious threat to aircraft.
Heathrow normally hosts around 1,300 flights and 180,000 passengers every day, while Gatwick would expect to handle 679 flights carrying 80,000 passengers. Yesterday, only 168 flights passed through the Sussex airport.
At Heathrow, travellers dragged their luggage around the terminals, many of them queuing at customer information desks in a bid to rearrange flights. Lines also formed for payphones and the internet as people attempted to contact relatives and find out more information.
Many were angry that all flights had been cancelled, with some saying the Nats decision was an over-reaction.
David Lees, 51, a businessman who was due to fly to Shanghai with a colleague, said the trip had been "completely disrupted" by the volcanic eruption.
"We couldn't even fly from Manchester this morning so we have already had to shell out £300 for a train," he said. "It's a total nightmare, but what can you do?"
There were similar scenes at Gatwick. Johann and Carrie Sikora, from Kent, had been due to fly to Verona at noon, for the wedding of two friends on Friday. She is the bridesmaid, while he is the best friend of the groom. "It's not really sunk in yet, but I'm gutted," said Johann.
He was however, phlegmatic about the reason for the disruption: "If we'd missed the flight because of the traffic I'd have been have been disappointed, but this morning when I turned the TV on I couldn't believe my eyes." The couple said they would try to reach Verona by train.
Airlines, insurance companies, the Civil Aviation Authority and the EU all reminded passengers of their compensation rights following cancellations. Those who were unable to fly today – and anyone in the same position tomorrow – should be offered either a refund or the option of rebooking on a new flight by their airline.
If the flight was part of a package deal, and the alternative flight offered would make a big difference to a holiday, travellers should be entitled to cancel the whole deal and get a refund. However, those who have booked only a flight will not be eligible for a refund from the airline for money lost on accommodation or transport arranged at their destination.
Anyone travelling on Friday is advised to check the status of their flights on the internet or contact the airline directly.
The upheaval caused by the ash cloud could also have serious implications for the economy. The British Chambers of Commerce said the cancellation of thousands of flights in and out of the UK would not help the country emerge from the global economic downturn.
"This is the right action to take," said David Frost, the group's director general. "However, it comes at a difficult time. Business is just recovering from deep recession and we are seeing for the first time in some years an improvement in our exports. Our recovery depends on British business searching out new overseas markets and getting cargo across the globe."
Patricia Yates, director of strategy and communications for VisitBritain, described the cloud as "a truly unexpected event". She said: "As for economic impact such a short-term measure would tend to balance out with some inbound visitors unable to arrive but others enjoying an extra day of our sunshine and spending in our hotels, restaurants and attractions."
Despite the chaos caused by the cloud, a volcanologist stressed that it posed no threat to people's health. "Ash can cause serious health problems but the high altitude of the current plume above the UK means it is air traffic and not humans on the ground that will suffer," said Dr Dougal Jerram of Durham University's department of earth sciences.
File:Eyjafjallajökull volcanic ash 17 April 2010.png|thumb|right|Approximate depiction of the estimated ash cloud at 18:00 UTC on 17 April 2010. The current forecasts are updated at  London Volcanic Ash Advisory Centre site (Met Office, UK).

Area in which aviation was endangered by volcanic ash. Situation estimated for April 15, 2010 at 18:00 UTC.
Hundreds of thousands of air travelers had their travel plans disrupted in Europe by volcanic ash from the Eyjafjallajökull eruption.

Tens of thousands of air travelers were stranded when all flights into and out of the United Kingdom were grounded, as it became one of the first nations to be affected. The grounding was even more extensive than that following the September 11 attacks of 2001 when only trans-Atlantic flights were canceled.

Eurocontrol released a statement saying "...most air traffic in the United Kingdom, Ireland, Denmark, Norway and Sweden is suspended."

The grounding is because the volcanic ash drawn into the jet stream is of a particle size which allows it to remain aloft in the atmosphere. Ingestion of this foreign matter, because of its distribution, would lead to flame outs in all aircraft engines. The composition of the ash also means that it would first melt into glass if it were to enter the engine of an aircraft before solidifying again as it cooled. This could lead to damage to the compressors and fan blades, which would make it impossible to restart the engines, even if the aircraft were to exit the cloud. 

The current contingency is informed by the experience of British Airways Flight 9, which on June 24, 1982 suffered just such complete engine flame outs when it flew through the plume of Mount Galunggung in Indonesia.  In that case, the flight crew after many efforts was able to restart the engines, though one failed shortly after, and the aircraft landed without casualties.

The UK National Air Traffic Services (NATS) has stated that "restrictions will remain in place in UK controlled airspace until 1300 (UK time) tomorrow, Friday 16 April, at the earliest," and that "We will review further Met Office information and at 0230 (UK time) tomorrow we will advise the arrangements that will be in place through to 1800 (UK time) tomorrow." The NATS statement concluded "...the situation cannot be said to be improving". 

In addition to Northern Europe, the ash is drifting south; Berlin and Hamburg airports in Germany are closed, and airports in the Netherlands, Belgium and Northern France are described as now being closed or closing.  Some flights from Spain and Portugal, together with upwards of 4,000 flights across Northern Europe, have been affected, and the knock-on effect of aircraft and crews out of position could disrupt air travel worldwide for up to 72 hours.

One affected group are British musicians booked to play at this weekend's Coachella Festival in California. Amongst those stranded are Frightened Rabbit, Gary Numan, The Cribs and Bad Lieutenant.