Britain's skies have reopened but passengers are still experiencing widespread delays.

Hundreds of flights had to be cancelled or delayed on Monday morning, with Heathrow and Gatwick among the airports affected.

By 1pm all but the most northerly Scottish island airports were operating normally again as the threat moved away. The no-fly zone for the period until 7pm remains in place only in the Orkney and Shetland Islands.

But delays continued, with some long-haul flights due in at Heathrow not expected to arrive until early on Tuesday.

The closures came after air traffic control company Nats warned that the cloud of ash from Iceland's Eyjafjallajokull volcano was spreading over the UK.

But airline bosses criticised the systems currently used to calculate the amount of ash in the atmosphere. British Airways chief executive Willie Walsh said blanket bans on flying were "a gross over-reaction to a very minor risk".