Thousands of passengers have had their flights cancelled because of drifting ash from an Icelandic volcano.
About 500 flights were cancelled in Europe on Tuesday, air traffic management body Eurocontrol said.
Flights from some airports in Scotland and northern England would be affected until 0100 BST on Wednesday, air traffic services company Nats said.
But the transport secretary said there should not be significant disruption for UK airports after Tuesday night.
Services at Glasgow, Edinburgh, Newcastle, Barra, Prestwick, Cumbernauld, Tiree, Carlisle and Durham Tees Valley could be affected until early on Wednesday.
UK air traffic control service Nats said the latest information from the Met Office showed no volcanic ash was predicted in UK airspace from 0100 BST on Wednesday.
Nats said further updates would be made if the situation changed and passengers are advised to continue to check with their airline before travelling.
Meanwhile, Germany's Meteorological Service says airspace over the country's northern cities, including Bremen and Hamburg, will close from 0400 BST (0500 local time) because of elevated levels of ash in the atmosphere.
The UK's emergency response committee, Cobra, met earlier to discuss the knock-on effects of the ash cloud.
After the meeting, Transport Secretary Philip Hammond said there was cautious optimism for the coming days.
He said the ash plume had decreased in height and intensity, and south-westerly winds were predicted for the next two days which would move the cloud away from the UK.
The Civil Aviation Authority (CAA) divides the airspace into areas of high-, medium- and low-density ash, and airlines wishing to fly in areas of medium- or high-density ash need to get a safety case accepted by the authority.
It said earlier that, although no airlines had applied to fly in high-density ash, some had applied for, and been given, permission to fly in medium density.
Mr Hammond said British Airways had been talking to the CAA to get permission to fly in higher density ash cloud zones in certain circumstances.
BA sent up a plane to test the ash on Tuesday evening.
An Airbus A320 left Manchester to fly over Newcastle, Glasgow and Edinburgh before heading to Heathrow airport where the plane and its performance will be examined by engineers.
Mr Hammond rejected claims by Irish carrier Ryanair that it would have been safe to continue flying in the areas of higher density ash cloud.
"We're quite prepared to talk to airlines about ways in which we can improve the regime on the basis of a properly demonstrated safety case," he said.
"But we're not going to be bullied by airlines or by anybody else when our primary responsibility is the safety of aircraft in British airspace and passengers leaving British airports."
Ryanair said it had safely made a test flight through ash over Scotland.
The airline said its 90-minute flight at 41,000ft showed there was "no visible volcanic ash cloud or evidence of ash on the airframe, wings or engines".
But a CAA spokesperson said: "The CAA can confirm that at no time did a Ryanair flight enter the notified area of high contamination ash over Scotland this morning."
The following airlines announced cancellations in the UK on Tuesday:
- British Airways was not operating any flights to and from Glasgow, Edinburgh and Newcastle
- KLM cancelled flights to and from Aberdeen, Glasgow, Edinburgh and Newcastle as well as from Durham Tees Valley Airport
- Aer Lingus cancelled 12 flights to and from Glasgow, Aberdeen and Edinburgh
- Flybe cancelled 11 flights to and from Scotland
- BMI cancelled all flights from Edinburgh and Glasgow for the rest of Tuesday
- Loganair, based in Glasgow, cancelled 38 flights. Only inter-island routes in Orkney are unaffected
- Eastern Airways was not operating any services in or out of Scottish airspace
- Easyjet cancelled flights to and from Edinburgh, Glasgow, Inverness, Aberdeen and Newcastle
- Ryanair cancelled all flights to and from Scotland for the rest of Tuesday
Airports affected included Londonderry, Glasgow, Edinburgh, Prestwick, Durham Tees Valley, Newcastle and Carlisle.
Passengers had been waiting at affected airports in the hope of getting flights.
At Glasgow airport, Guy McKinven, from the Clyde Valley area, was attempting to travel to Stansted.
He said: "You see people shouting and getting upset, but there's nothing you can do. It is frustrating, but that's just the situation."
The cancellations come just over a year after another volcanic eruption in Iceland caused widespread disruption across Europe, including the closure of UK airspace, amid concerns about the damage volcanic ash could cause to engine aircraft.
The Grimsvotn volcano in Vatnajokull National Park began erupting on Saturday and closed Iceland's airspace for a period.
Experts say the eruption is on a different scale to the one last year and ash particles are larger and, as a result, fall to the ground more quickly.
Frances Tuke, from travel industry body Abta, urged passengers to contact their airlines, which he said had legal obligations to their customers.
He said passengers could have a claim under European "denied boarding" regulations.
These state that if a flight is cancelled or delayed for more than five hours, passengers are entitled to be either re-routed, given a replacement flight, or a refund.
The Foreign Office is advising passengers to remain in regular contact with their travel agent or airline for the latest news on the status of flights and bookings.
Icelandic government adviser Professor Magnus Tumi Gudmundsson said the volcanic eruption was slowing down "day by day" and he believed the "worst is over".