Different parts of airspace including the south east, where Europe's busiest airport Heathrow is located, are likely to be closed at different times, the Department for Transport said.

"Due to continuing volcanic activity in Iceland and prevailing weather conditions, there is  if the volcano continues to erupt at current levels a risk of UK airspace closures," it said in a statement

If restrictions become necessary, an announcement will be made by the National Air Traffic Service, it added.

The spread of ash from an erupting volcano under the Eyjafjallajokull glacier in Iceland grounded much of European air traffic for nearly a week in mid-April. Airlines had to cancel around 100,000 flights, stranding millions of passengers.

Since then the ash has periodically forced short-term closure of parts of airspace in countries across Europe, including Spain, Portugal, Ireland and Germany.

British Transport Minister Philip Hammand said on Saturday that from now on five-day - rather than the previous 18-hour - ash prediction charts would be made available to airlines and the public on the Met Office forecaster's website.