London, May 25 (IANS) Thousands of passengers were stuck at airports across Britain as 500 flights were cancelled due to the Icelandic volcano eruption.

Passengers were stranded at different airports, including Heathrow, Newcastle, Glasgow and Edinburgh, reported The Sun.

Transport Secretary Philip Hammond said airports in Britain should return to normal Wednesday as the ash cloud went down from 12 miles to just two.

He said a special aircraft had been bought to test the intensity of ash levels. The aircraft, however, would not be operational until next month or early July.

Airlines which axed flights to and from Scotland Tuesday included British Airways, bmi, Aer Lingus and KLM.

The ash cloud was likely to clear out of most of British mainland Wednesday.

The towering ash cloud had forced visiting US President Barack Obama to leave Ireland for Britain one day ahead of schedule over safety concerns.

Xinhua quoted Europe's air traffic control organization Eurocontrol as saying that around 500 flights have been cancelled from the approximately 29,000 that would have been expected Tuesday across Europe due to the eruption of the Icelandic volcano.

Area of high ash concentration were over northern Britain, the Brussels-based organization quoted the Volcanic Ash Advisory Center (VAAC) in London as saying.

According to VAAC predictions, there is a "strong possibility" that the ash may impact parts of Denmark, southern Norway and southwest Sweden by Tuesday, said Eurocontrol.

The Grimsvotn volcano, which lies beneath the ice of the uninhabited Vatnajokull glacier in southeast Iceland, began erupting Saturday for the first time since 2004, shooting ash, smoke and steam up to 20 km into the air.

Although the eruption was much stronger than the one at a volcano further south in 2010, experts said they saw little chance of a repeat of last year's six-day closure of airspace.

Volcanologists said the ash cloud's content was heavier and less likely to spread this year.