The European air traffic agency Eurocontrol said that between 200 and 250 flights have been cancelled in Europe.
The disruption is expected to spread to some northern England airports later today.
The eruption of the Grimsvotn volcano has already led to airlines cancelling a number of flights to and from Irish and Scottish airports.
Shortly after 9.30am today, air traffic control company Nats said "an area of volcanic ash" was forecast to affect some parts of the UK between 1pm and 7pm today.
Nats said airports remained open but that services from Londonderry, Glasgow, Edinburgh, Prestwick, Newcastle, Carlisle, Durham Tees Valley and Cumbernauld airports may be affected.
Nats said passengers should check with their airline before travelling to these airports.
The airports listed by Nats could all possibly experience high- level densities of ash.
Earlier Nats had said air services at Aberdeen, Inverness, Benbecula, Barra and Tiree airports could be affected until 1pm. The latest bulletin from the company suggested that these airports might be free of ash later today.
In the meantime, airlines have already axed many flights to and from Scotland, with British Airways not operating any flights between London and Scotland before 2pm.
Scots regional airline Loganair scrapped 38 flights and Irish carrier Aer Lingus said it had cancelled 12 flights to and from Glasgow, Aberdeen and Edinburgh.
British Airways announced that it would not operate any flights between London and Scotland before 2pm.
EasyJet also cancelled its flights from Glasgow until lunchtime.
At Glasgow today, most passengers whose flights had already been cancelled did not make their way to the airport.
Passengers with holiday companies Thomson and Thomas Cook were waiting for buses to take them to Manchester to pick up later flights.
The airport's cafes were packed and people sat on their suitcases or tried to catch up on sleep as they waited for news.
Guy McKinven, from the Clyde Valley area, was travelling with easyJet to Stansted to spend a week with his grandmother.
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. EasyJet have been helpful and have told me I can have a refund for my flight.
Despite the flight cancellations today, there were hopes that the latest crisis would not have the same devastating impact as last year's Icelandic volcanic eruption which saw UK airspace shut down and thousands of air services axed.
Transport Secretary Philip Hammond said: "There is some early indication that the scale and power of the eruption might be subsiding a little bit.
"Perhaps it's a little bit too early to be absolutely sure about that, but clearly that's the most important thing. If the ash stops belching out of the volcano then, after a few days, the problem will have cleared, so that's one of the factors.
"The other is the wind speed and direction. At the moment the weather patterns are very volatile which is what is making it quite difficult, unlike last year, to predict where the ash will go."
He added that the public should be assured that airlines would only operate when it was safe to do so.
Ryanair said it carried out a one hour flight 41,000ft over Scotland this morning in the so-called "red zone" of the ash cloud from Glasgow Prestwick to Inverness, on to Aberdeen and then south to Edinburgh.
Aviation chiefs have deemed Scottish airspace "high ash concentration".
Ryanair said there was no visible volcanic ash cloud or any other presence of ash and post flight inspections revealed no evidence of ash on the airframe, wings or engines.
The low-cost carrier claimed the red zone was non-existent, mythical and a misguided invention by the UK Met Office and the Civil Aviation Authority (CAA).
Ryanair said it has written confirmation from both its airframe and engine manufacturers that it is safe to operate in the area.
"This morning's verification flight has demonstrated that the UK Met Office's 'red zone' forecasts are totally unreliable and unsupported by any evidence of volcanic ash concentrations whatsoever," Ryanair said.