A new ash cloud spreading towards the UK is causing uncertainty over plans to reopen some airspace on Tuesday, air traffic control body Nats has said.
Earlier, it said the flight ban would be lifted over Scotland, Northern Ireland and the north of England.
But Nats said there was now a worsening situation in some areas. The outlook for Northern Ireland is most uncertain.
Scottish airports are still expected to reopen from 0700 BST, but Nats said it would report again at 0300.
A further update will be made at 0900 BST on Tuesday.