LONDON - Britain is bracing for what scientists warn could be weeks of disruption after predictions the volcanic dust cloud blanketing Europe will cause chaos for the foreseeable future.

As reports emerged of ash landing in southeast England, meteorologists said volcanic activity in Iceland's Mt Eyjafjallajokull increased yesterday, forcing officials to extend flight restrictions yet again in an unprecedented air lockdown over much of Europe.

With no sign of the eruption easing, volcanologists said the ash, which is drifting in a cloud extending up from 8000-30,000 feet (2438-3657m) and stretching across much of northern and central Europe, could disrupt flights for up to six months.

Airlines cancelled thousands more flights this weekend, prolonging misery for millions of people.

Graeme Leith, who heads the Met Office's defence forecasting service, said: "This is Mother Nature. We're stuck in this phase until the volcano decides to sleep. Even if it cuts off today, which it shows no sign of doing, the ash would take another two to three days to fall out from the skies."

Icelandic geologist Magnus Tumi Gudmundsson said: "The activity has been quite vigorous overnight, causing the eruption column to grow. It's the magma mixing with the water that creates the explosivity. There doesn't seem to be an end in sight."

After studying webcam images of the volcano's eruptions, Dr David Rothery of the Department of Earth & Environmental Sciences at the Open University said it appeared fine ash was being drawn to high altitude and blown towards Britain.

"While this situation and the present wind conditions persist, I think it unlikely the restrictions placed on air traffic are going to be eased," he said.

Met Office forecasters said it would take a prolonged change of wind direction for the situation to improve. "The UK and much of Europe is under the influence of high pressure, which means winds are relatively light and the dispersal of cloud is slow. We don't expect a great deal of change over the next few days," Leith said.

Volcanologists are worried the eruptions could set off a sister volcano, Katla, which is much bigger. Because Eyjafjallajokull is below a glacial ice cap, the magma is being cooled quickly causing plumes of grit that can be catastrophic to plane engines if prevailing winds are right, scientists said.

Sigrun Hreinsdotti, a geophysicist at the Faculty of Earth Science at the University of Iceland, warned: "Even if this stops right now we don't know if that's the end of the story. More magma pressure could build up and erupt elsewhere, possibly under Katla, which has a much bigger glacier so would be much more explosive."

Fallout from the vast ash plume stranded travellers around the globe. Delta Airways, Qantas, Virgin, British Airways and Cathy Pacific were among airlines to extend flight cancellations.

British Airways, which cancelled all long and short-haul flights into and out of Britain yesterday, said it had no firm contingency plans to deal with the passenger backlog.

Volcanic ash started falling out of a clear, bright sky in west London, with residents in Chiswick reporting dust on their cars. Scientists are now testing the deposits to see if they pose any health risks. Initial tests from three samples tested at Aberdeen, Lerwick and East Kilbride by the Scottish Environment Protection Agency suggested any risks were "minimal".

Consumers were warned that shops could start running low on supplies of fresh vegetables and fruit, and analysts said economic costs could spiral.

Howard Archer, chief European economist at IHS Global Insight, said "the longer that the problem persists, the more serious will be the economic repercussions".

British and Irish scheduled airlines are losing up to £28 million ($60.6 million) a day, with the total bill to European carriers hitting US$200 million ($282 million), according to the International Air Transport Association.

One of the Britain's biggest fresh fruit importers said business had ground to a halt. Anthony Pile, chairman of Blue Skies, said the company was losing £100,000 a day.

More than three-quarters of flights were lost yesterday across Europe, with barely 5000 taking off or landing, the Eurocontrol air traffic agency said. This compares with a typical 22,000.

Around Europe, 73 transatlantic flights landed yesterday morning, less than a third of the 300 that would normally arrive. The situation deteriorated from Saturday, when 10,400 flights made it out of the normal 28,000.

Consultancy firm KPMG estimated there had been a £200 million loss in traffic revenues so far as a result of the UK shutdown. The International Air Transport Association said its members would also lose money as a result of expensive contingency plans. "In addition to lost revenues, airlines will incur added costs for rerouting of aircraft, care for stranded passengers and stranded aircraft at various ports," said spokesman Anthony Concil.

One pilot on the Professional Pilots Rumour Network website offered a bleak prognosis: "If we're not back in the air by Wednesday we start to fire people."

Air freight represents just 1 per cent of the UK's trade by weight. However, in value terms, around 30 per cent of exports are transported by air, with the pharmaceutical industry particularly reliant on air freight.

Passengers anxious to get home are inundating the ferry companies. Most P&O crossings are booked until Thursday.

A British businessman stranded in France said he was forced to buy a bicycle to board a ferry in a bid to get home for his wife's birthday.

Tom Noble, 52, from London, said ferry operator Norfolkline had no foot passenger tickets left and would allow him to make the journey only if he were a genuine cyclist. The managing director said ferry staff even made him ride the "rustic" contraption, which he had bought from a second-hand shop.

"You have to show you haven't just picked one up from anywhere."

Another passenger, David Flashman, said there were 40-minute queues of cars just to get to the ticket booths at Dunkirk docks: "Desperate travellers trying to get back to Britain were begging for rides. Some pleaded, some offered cash, others tried to bribe their way into other people's vehicles with cartons of cigarettes.

"One Polish guy who had a hoard of cigarettes in his estate car was selling them at a premium to these business blokes so that they could then use them to bribe their way into other cars."

All 58 of Eurostar's high-speed trains out of London were full yesterday. The company's offices at St Pancras International station were shut and only people with e-tickets were being served.

Office workers Ellen Stanic, 49, and Christina Simon, 50, both from Dusseldorf, said they had been trying to leave Britain for three days. "We couldn't get tickets for the Eurostar, so we go to Dusseldorf by bus tonight," Stanic said. "And there's no way of claiming back our money, it's an act of God. We've lost a lot of money - about £600 or £700 in total."

London minicab company Addison Lee said it had received requests to take passengers to cities as far away as Paris, Milan and Zurich.

Yesterday, English airports were largely deserted but knots of passengers, unaware of the blanket ban, turned up to find empty check-in desks. At Heathrow, flight dispatcher Anthony Adeayo, 45, who was due to travel to Nigeria with British Airways, said cash flow was his major concern. "I've been staying in a hotel but have now checked out and don't know what I am going to do - I have limited financial resources," he said.