The Icelandic ash cloud has moved south again, leading to the closure of most airports in England's north and Midlands as well as across Ireland and parts of Scotland.
An aviation expert in the UK says travel disruptions could continue for up to 20 years.
London airports remain open at least until tonight Australian time but travellers are being urged to check with their airlines.
A no-fly zone has been imposed over many parts of Scotland, all of Northern Ireland, northern England and the Midlands.
Manchester Airport in north-west England and Dublin Airport, among the 20 busiest in Europe, were among those affected by the cloud, with the ash levels deemed too dangerous to fly through.
Dublin, Ireland's main airport, was to close from 6:00pm GMT Sunday (4:00am Monday AEST) until at least 8:00am GMT on Monday.
Europe's skies were partially closed for up to a week last month following the eruption of Iceland's Eyjafjoell volcano in the biggest shutdown of the continent's airspace since World War II.
The volcanic ash can cause serious damage to jet engines.
In England, several other airports were shut until midnight GMT Monday as the no-fly zone extended southwards.
They included regional air hubs Birmingham, East Midlands, Liverpool, Leeds-Bradford, Doncaster, Durham Tees Valley, Norwich and Humberside.
In Scotland, the main Edinburgh and Glasgow airports were open but the fourth busiest, Prestwick, and some island airports were shut down, while all Northern Ireland airports closed for the period. The Isle of Man airport was also shut.
