Chief Superintendent Gordon Urquhart of Northern Constabulary said today that, based on the encouragement given by Professor Black and an expert from Birmingham University, contractors moved on to the former Dalmagarry Quarry off the A9 today.

“The quarry has been filled in and covered with trees, which are 20 feet tall. Contractors have today begun felling the trees on the four hectare site to allow a further investigation to begin.

“It should take about two weeks to remove the trees. Professor Black and her colleague have already visited the site and will return on August 23, when we start to dig up the quarry, to advise us.

Based on what they have told us so far, we think there is a good chance the quarry is where the bodies are buried.”

Professor Black, who leads Dundee University’s department of forensic anthropology, declined to be interviewed on the inquiry today and referred all calls to Northern Constabulary. She came to international prominence through heading the British team in Kosovo, which investigated mass graves.

The disappearance of Mrs Macrae and her young son after her burning BMW car was found on a lay-by on the A9 south of Inverness in 1976 is one of Scotland’s most baffling cases.

Their bodies have never been found, but, because of the circumstances, police said some time ago they were engaged in a murder inquiry rather than a missing persons’ investigation.

The trail had gone cold until Grampian Television featured the case in their Unsolved : Getting Away with Murder series earlier this year.

Their programme revealed that a former sergeant was suspicious that the bodies may have been buried in Dalmagarry Quarry because he thought he smelled rotting human flesh on the site. However, his request for the land to be excavated was over-ruled by a superior officer.