Europe's skies were open for business on Wednesday but with so many planes having been grounded by the pall of volcanic ash spreading from Iceland it could take days or weeks to clear the backlog.

Britain, a global air hub as well as a busy destination in its own right that has been squarely under the ash plume, reopened its airspace on Tuesday night, giving a huge boost to travellers and air freight.

British Airways said it would operate all its long-haul flights departing from Heathrow and Gatwick airports on Wednesday, but there would be short-haul cancellations to and from London airports until 1 pm (1200 GMT).   

Britain's Civil Aviation Authority made clear that scientists and manufacturers had downgraded the risk of flying in areas of relatively low ash concentrations.   

'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,' CAA head Deidre Hutton said.

Air France plans to run all long-haul flights on Wednesday, Poland will reopen its airspace from 0500 GMT, and the Dutch allowed night flights from Tuesday after taking the lead in allowing passenger flights on Monday.

German air traffic control said German airspace would be open by 0900 GMT, a spokesman said. But of 60 flights listed on the Frankfurt airport website on Wednesday, 46 were cancelled.   

Flights from Beijing and other Chinese cities to European destinations began to return to normal Wednesday. Air China, the country's main carrier, said on its website its 'flights to Europe have been fully restored' from Wednesday.

The airline warned, however, that it would keep in contact with European aviation authorities about weather conditions and could alter flight plans if warranted.

Britain had lagged its European neighbours in downgrading the threat to airplanes from the ash, which can potentially scour and even paralyse jet engines.

In 1982 a British Airways jet lost power in all four engines after flying through an ash cloud above the Indian Ocean.

With aircraft having flown successful test flights for several days, recriminations have started about what took governments so long to give the green light to an airline industry which according to the International Air Travel Association (IATA) lost some $1.7 billion.
   
The head of Iata urged governments to examine ways to compensate airlines for their lost revenues.

'It is an extraordinary situation exaggerated with a poor decision-making process by national governments,' Iata Director General and CEO Giovanni Bisignani said in a statement.

Airlines did however save around $110 million a day on costs such as fuel, Iata said.   

The Association of European Airlines, representing 36 major commercial and freight carriers, criticised Britain on Tuesday for not reopening its skies sooner.

'Other people look to the UK and say 'Why are they still cautious when we are thinking of opening up?,' and of course this can influence judgments,' David Henderson, AEA manager of information, told Reuters before Britain lifted its no-fly zone.

Icelandic officials said on Wednesday the volcano under the Eyjafjallajokull glacier was still erupting, but producing much less ash.   

An expert from the World Meteorological Organisation said in Geneva that a low pressure weather system moving into Iceland should help clear the ash cloud within days.

For the airline industry, which said its losses from the shutdown were worse than after the Sept 11 attacks on the United States, freeing up the flights is a welcome relief. But with aircraft and crew scattered where they were grounded on Thursday, timetables will be wrecked.   

'To get back to normal levels of operation from an industry point of view will take weeks,' British Airways chief executive Willie Walsh told BBC television.

Steve Ridgway, chief executive of Virgin Atlantic, said: 'Whilst the reopening of airspace is good news both for passengers and the industry as a whole, it is likely to take several days to get everyone who has been affected to their destinations.'  - Reuters