Airports around Britain have suffered major flight disruption after the return of the Icelandic ash cloud caused chaos for thousands of passengers.

A no-fly order saw the UK's two busiest airports, Heathrow and Gatwick shut until 7am on Monday, with both only partially due to reopen over the next six hours, air traffic authority Nats said.

Flights have also been grounded until lunchtime across Northern Ireland and much of Scotland and Wales, with warnings of widespread knock-on disruption later in the day both in the UK and abroad.

No arrivals are expected at Gatwick until 1pm at the earliest, while Heathrow will see reduced take-offs and departures as well as extended delays and cancellations.

Some big regional airports like Manchester, Glasgow and London Stansted are open, but passengers everywhere have been urged to check with their airlines before leaving for the airport.

Nats warned the ash cloud was "continuing to change shape" as it spread over southern England to Northern Ireland and as far north as the Shetland Isles.

The latest air travel chaos comes a month after the Eyjafjallajokull volcano eruption cancelled a swathe of flights across Europe, and as talks continue to avert a crippling five-day strike by British Airways cabin crew.

There are warnings that the ash restrictions could persist in the UK until Tuesday. Forecasters are expecting a change in the north-westerly wind direction, which is expected to blow the "high density" cloud from the volcano away from Britain on Tuesday.

Earlier revisions to the no-fly zone meant airports in the north of England like Manchester, East Midlands and Leeds Bradford reopened from 1am on Monday, after being closed for most of Sunday.

But Manchester Airport warned: "It is absolutely essential that people contact their airline before travelling to the airport for any flight because there are still high levels of ash contamination above parts of Britain which may bring further disruption."

Stansted, Luton and East Midlands airports also said they were operational, but all were urging passengers to contact their airlines before setting off.

In Scotland, Prestwick Airport was no longer in the no-fly zone but a spokeswoman said it would not be receiving any flights up until 12.45pm on Monday. Glasgow airport also said it was open, but warned of knock-on disruption from the other closures, while Aberdeen said it would be shut until at least 1pm.