Volcanic ash which spewed from an eruption in Iceland over the weekend will spread across the British Isles by the end of the week or perhaps earlier, according to forecasting reports.

Scottish airline Loganair has cancelled 36 flights in response to the threat from the volcanic ash.

In a statement the airline said: We have taken the decision to cancel all services with the exception of our inter-isles flights in Orkney. All flights due to depart between 06:00 and 13:00 hrs tomorrow have therefore been cancelled. You should not travel to the airport and if you are booked on a flight departing tomorrow afternoon, you should check the website for further updates before setting out for the airport.”

NATS, the air traffic control group, said three small airports in Scotland -- Barra, Benbecula and Tiree – will be immediately disrupted.

The Civil Aviation Authority (CAA) warned that more flight disruptions were possible.

It depends how thick the cloud is and how big it is, said a CAA spokesman.

If it is so big that it makes it impossible to get in or out of an airport, then flights will be cancelled. But if we are talking about small thick pockets, then it should be possible to fly around them. It won't be until late tonight that we have a real idea what the impact will be and passengers should contact their airlines to keep up to date.

British aviation authorities said they are monitoring the situation closely.

We can’t rule out disruption, said Andrew Haines, the CAA's chief executive, according to the Daily Telegraph.

But the new arrangements that have been put in place since last year’s ash cloud mean the aviation sector is better prepared and will help to reduce any disruption in the event that volcanic ash affects UK airspace.”

The eruption of the Grimsvotn volcano – which is sending plumes of smoke 12 miles into the air – comes about one year after an eruption by the Eyjafjallajokull volcano disrupted air travel over much of Europe, cancelling thousands of flights.

A spokesman for Europe's Volcanic Ash Advisory Centre told reporters: This is a very different situation to last April. The weather is much more changeable and there's a lot more uncertainty. There's no risk of the ash moving across the UK in the next day or so. But there is a possibility that we'll see some volcanic ash towards the end of the week.

Pall Einarsson, a geophysicist at the University of Iceland, told British media: It is not likely to be anything on the scale that was produced last year when the Eyjafjallajokull volcano erupted. That was an unusual volcano, an unusual ash size distribution and unusual weather pattern, which all conspired together to make life difficult in Europe.

Professor Gillian Foulger, Department of Earth Sciences at Durham University, told the Telegraph: “This eruption is bigger and more spectacular than the Eyjafjallajökull eruption. Its gigantic initial volcanic plume suggests that it may exhaust itself and cease quicker than the Eyjafjallajökull eruption, but only time will tell.

Meanwhile, air traffic officials in Iceland have imposed “no-fly zone” around the Grimstovn volcano, closed Keflavik airport and cancelled all domestic flights.