London - 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 $1.7bn 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.