About 250 flights to northern Britain were cancelled on Tuesday over concerns about the ash cloud spewing from an Icelandic volcano, but British and Irish officials dismissed fears of a mass shutdown of airspace.

The explosion of the Grimsvotn volcano has raised worries of a repeat of the volcano-related travel chaos that stranded 10 million passengers and cost the air industry an estimated $1.7 billion in lost revenue last year.

Airline officials have said changes to rules on how airlines and civil aviation authorities decide on the risks of flying should have the effect of reducing disruptions to travel compared to last year.

European air traffic agency Eurocontrol said 250 flights had been cancelled in British airspace as the ash cloud has drifted lower from Iceland, however.   

US President Barack Obama left Ireland for Britain late on Monday ahead of schedule, and Barcelona soccer coach Pep Guardiola said he was weighing coming to London early for Saturday's Champions League final against Manchester United. But officials rejected the idea of a general flight ban.

'There won't be any shutdowns,' British Transport Secretary Philip Hammond told BBC radio. 'We've moved on to a different way of working, we won't be closing airspace.'    

'Even though there will be ash present over large parts of the UK for parts of this week that will not stop flying activity.'    

Eurocontrol has said that if the volcanic emissions continued at the same rate, the cloud could reach western French and northern Spanish airspace on Thursday. President Nicolas Sarkozy is due to host Obama and other G8 leaders in northern France this week.

The Irish Aviation Authority also said it would not shut any airports, but Ryanair, which listed 36 cancellations between Scotland and cities across Europe, complained the Irish authority had stopped it flying to Scottish airports until at least 1 pm (1200 GMT).   

'Ryanair believe that there is no safety risk to aircraft on flights operating to and from Scotland ...,' it said in a statement about what it called 'unnecessary cancellations'.   

The airline's pugnacious boss, Michael O'Leary, was a vocal critic of the restrictions imposed on airlines last year out of concern that ash particles could cause engine problems.

He had said on Monday he was cautiously optimistic that regulators would not 'balls it up again this year'.

A host of other airlines also cancelled flights to Scotland, including British Airways, EasyJet, Aer Lingus, KLM, part of Air France-KLM, and Nordic airline SAS. Shares in airline companies, which fell on Monday, were steady to slightly lower.   

Eurocontrol said the ash could affect flights in parts of Denmark and southern Scandinavia on Tuesday. Norway's airport operator said the ash cloud would cause some flight restrictions on its west coast while helicopter supply services to North Sea oil operations from Stavanger and Karmoey airports also faced disruption. Denmark said a small area of its airspace would be closed.   

Ironically, Iceland's main international airport, Keflavik, was operating after being closed at the weekend and most of Monday, but several flights to Britain had been cancelled. In Iceland, Hjalmar Bjorgvinsson, superintendent at the national police, said the height of the ash cloud had fallen to about 3 to 6 km from about 10 km (6 miles) on Monday.
   
However, an official at the Icelandic Meteorological Office said tremors at the volcano were continuing, making it too early to say the eruption was losing power. Grimsvotn erupted on Saturday and smoke belched as high as 20 km (12 miles) into the sky.

The eruption is the volcano's most powerful since 1873 and stronger than the volcano that caused trouble last year. - Reuters