THE son of a world-renowned Scottish geologist has demanded police protection as he prepares to testify at the trial of the men alleged to have murdered his father.

Campbell Bridges, 71, who was also a gemstone expert, died in an ambush by 30 assailants armed with clubs, spears, bows and arrows on his 600-acre estate in Kenya three years ago.

On Thursday in Mombasa, the trial of seven men is due to get under way.

Mr Bridges's son, Bruce, 33, who survived the attack, is due to fly in from his home in the US to give evidence. At a pre-trial hearing, the city's High Court heard he has pledged not to return to the country unless his security can be guaranteed.

Counsel for Bruce Bridges claimed his father, who made one of the most important gemstone finds of the 20th century when he discovered the rare gemstone tsavorite, would not have died if his request for similar arrangements had been in place at the time of his death in August 2009.

The trial judge, Maureen Odero, directed the public prosecutor's office to provide security.

Bruce Bridges, his father and four of his staff fought off the gang, but Campbell Bridges was stabbed in the chest and died of his injuries on arrival at hospital following the incident near Voil, southern Kenya.

Mohammed Dadi Kokane, Alfred Njururuka, Samuel Mwachala, James Chacha, Osman Abdi, Crispinus Mkunguzi and Daniel Mdachi Mnene are accused of mobbing, rioting and murdering him.

However, the court case has wider implications for the country's Government.

The Bridges family has presented a report to the Kenyan Attorney General accusing Kenyan education assistant minister Calist Mwatela and gender minister Naomi Shabaan of interfering with investigations into the crime.

Campbell Bridges's mining company had been involved in a protracted dispute with a mining company owned by Mr Mwatela.

Ms Shabaan is accused in the report of shielding one of the accused men, Mnene, who is a relative of hers.

Police who investigated the attack confirmed it was connected to a three-year dispute over access and control of his mines.

Campbell Bridges, who was a senior jewel consultant with Tiffany and Company in New York, was raised in Zimbabwe and South Africa into a Scottish family. He was fiercely proud of his Scottish roots and had close contacts with the Scottish Gemmological Association.

His father was a geologist with the diamond exploration firm De Beers.

He spent his life on perilous hunts for some of the world's rarest stones.

Mr Bridges's life featured frequent brushes with snakes and scorpions, big cats and buffalo, and the story of his discovery of tsavorite has been described as a "Boy's Own" tale of risk and reward.

He was working for the UK Atomic Energy Authority in Rhodesia in 1961 when he surprised a buffalo while exploring on his day off.

The animal charged, and Mr Bridges was forced to dive into a gully. When he looked around him he noticed the sunlight glinting off greenish crystals in nearby rocks.

He said: "I had never seen a green like it. It was pure in every sense."

Six years later in "a small hidden valley in a rugged range of hills about 100km from Kilimanjaro which a large rhinoceros had made his home" he found another lode which yielded some of the largest tsavorites ever found.

The following year he traced deposits in southern Kenya.

Three years later his face was appearing on advertisements in the US for Tiffany and Co, which was keen to promote the as yet unnamed "tantalising jewel". It was later officially named tsavorite after Kenya's Tsavo National Park.

The trial is due to last two days.