A low-flying passenger jet over Warwickshire could have resulted in a potential disaster, experts said, heightening public fears over the expansion of Midland airports.

An Airbus A310, operated by Iranian passenger airline Mahan Air, was logged at 600ft - three times lower than required - above Warwickshire as it came into Birmingham International Airport at mid-day yesterday.

It was just six miles from the airport when air traffic control alerted the pilot. The aircraft had to do a go-around and land safely at the second attempt.

Last night, experts praised the quick-thinking air traffic controllers for averting a crash in the busy airspace over Kenilworth, also used by planes from Coventry Airport.

Opponents of the proposed increase in passenger operations at Coventry said it proved their fears were justified.

A spokeswoman for the Campaign Against Expansion at Coventry Airport said: "Do we have to see a near miss or potential disaster turn into reality before people realise our concerns are real and justified?

"This is an area that is also used by Thomsonfly jets using Coventry and an incident like this is even more likely to have turned into a disaster if the airport is allowed to expand its operations and more planes are in the sky more often."

BIA is the main objector at an ongoing public inquiry in Leamington Spa looking at the Coventry Airport plans. It believes there would be a potential airspace conflict between an expanded Coventry and increased traffic at Birmingham over the next decade.

Last night, the Department for Transport said the Air Accidents Investigation Branch (AAIB) had launched an investigation into the Airbus which had been flying from Tehran to Birmingham. A department official said: "AAIB officials have gone to Birmingham where the plane and its flight data recorder are being detained."

Aviation expert Chris Yates said: "At six miles out, the plane should have been coming in at about 1,800ft but seems to have been logged by air traffic controllers at 600ft. This could have been a dangerous incident."

In a statement, a BIA spokes-woman said: "We are aware of reports that an aircraft flew over the Honiley area at a low level on Thursday 23 February.

"This is now the matter of a full investigation for the Department for Transport."

Private pilot Glynn Edwards, from Barford in Warwickshire, said: "It is very strange that the instrument on a sophisticated plane like the A310 did not appear to warn the pilot he was at the wrong altitude. The risk of a catastrophe was huge."

The plane was spotted flying low over Honiley, near Kenil-worth, as it began its descent at about mid-day. A farmer in nearby Meer End rang the airport to say a plane had flown too low over his farm. John Conneally said he could see the plane's undercarriage out and ready for landing.

"It looked like it was only 200 to 300 feet up as it nearly hit the straw stack. It happened so quickly it was like a boom," he said. The plane then started to climb again, he said.

"The pilot on the plane must have seen us. We were looking after the cattle in the shed and the cattle went mad," he added.

Last night messages of praise for Birmingham air traffic control were left on a website used by professional pilots.

One poster said: "600 ft in an A310 over Honiley must have looked... interesting. Well done to that ATC controller for saving a potential disaster." ..SUPL: