An air ambulance crash which claimed the lives of three people was probably caused by a hidden overhead power cable, an official accident report has said.

The £2m Aerospatiale Squirrel helicopter crashed in July 1998 near Rochester, Kent, killing pilot Graham Budden, 40, and paramedics Tony Richardson, 47, and Mark Darby, 37.

The three had attended a road accident, having found on arrival their services were not needed. They were heading up a narrow valley towards Rochester airport when the helicopter hit the cable.

It went into a dive and crashed in a ball of flames, killing all three men instantly.

The report from the Air Accidents Investigation Branch, published on Thursday, said the cable's supporting pylons on each side of the valley were hidden by trees and the cables blended into the background of the fields.

Mr Budden, from Lingfield, Surrey, was therefore "most unlikely to have been able to see the cables in time to avoid them", said the report.

Cable replaced

A few days before the accident the former RAF pilot, who had served in the Falklands, told his wife Linda he was going to give up flying helicopters.

The report found no definite reason why the helicopter had flown up the valley at low altitude after "abruptly breaking off what appeared to be a normal approach to land at Rochester airport".

The AAIB said it could find no evidence anything had gone wrong with the aircraft before it hit the cable.

But the report added: "The possibility that a pre-accident problem had been present could not be dismissed in view of the absence of evidence in a number of areas resulting from the high level of fire-damage to the wreckage."

Since the accident the cable has been replaced and conical spiral markers have been added to the cables across the valley to make them more conspicuous.

The AAIB recommended the Civil Aviation Authority consider requiring UK helicopters to be fitted with cable-strike protection systems, which cost £17,000.

But it said it was uncertain whether such a system would have protected the Kent helicopter from catastrophic damage given the size of the cable involved.