A passenger plane heading for Heathrow reportedly came within about 100ft of a business jet in mid-air but managed to avoid a disastrous collision.

The planes may have been involved in the closest British near-miss, although no-one will know for certain until an investigation is carried out.

An air traffic controller has been suspended

The Boeing 737 and a Gulfstream IV were flying at 12,000ft over Chigwell, Essex at 1930GMT on Friday.

If reports of the incident prove correct, the two aircraft came very close to a mid-air collision, 12,000 feet in the air.

Aircraft merged

The Boeing 737 passenger jet was circling in the "holding stack" over Chigwell, waiting for clearance to land at Heathrow, when it was involved in the incident with a Gulfstream business jet bound for Farnborough in Hampshire.

According to reports, the radar images of the two aircraft were seen to merge on screen displays at the London air traffic control centre at West Drayton near Heathrow.

One report suggests a controller ordered the two aircraft to take avoiding action.

Another source told the BBC that a collision was only avoided after an alert from a Traffic Collision Warning and Avoidance System, known as TCAS, which was fitted on the business jet.

TCAS is increasingly installed on modern passenger aircraft, although it will not become mandatory for planes flying in UK airspace until next year.

Independent investigation

The independent investigators from the UK Airprox Board will seek reports from both pilots and all the controllers involved in the incident.

They will study tapes of radio conversations between the pilots and air traffic controllers and will examine radar recordings and read outs from separation monitoring equipment, to determine exactly how far apart the two aircraft were.

The investigators will also assess how serious the incident was and make any recommendations for safety improvements. Their report is expected to take six to nine months to complete.

The Civil Aviation Authority (CAA) confirmed that the controller involved has been taken off duty and asked to submit a written report.

Airmisses every year

It said this was normal procedure after an airmiss incident. The CAA added that about 40 possible airmisses were reported every year in Britain, and most were later found to have posed no risk to passengers.

The latest airmiss comes only days after an internal CAA document was leaked to the BBC, warning of growing pressures on controllers in the terminal control operations room at West Drayton.

It was this same part of the air traffic control centre that was involved in last Friday's incident. The CAA, which has an extremely good safety record, insisted that safety was not being put at risk.