The well liked Mason was gunned down with four other westerners and a Saudi by fellow employees at Exxon Mobil’s Yanbu refinery on the Red Sea.

Mason spent many years at Clough Ltd, being recruited to join the group in 1985, where he established an excellent personal and professional reputation.

A company spokesman said three employees working at the plant as security guards entered the site on Saturday, letting in a fourth accomplice through an emergency exit.

The group stormed into the offices of the Swiss-owned oil services company ABB Lummus and at point blank-range fired at workers, killing the men instantly.

It has now emerged that one of the gunmen was one of the Saudi Arabia’s most wanted terrorists.

Abdullah Saud Abu-Nayan al-Sobaie, believed to have masterminded the carnage, was killed in the shootout with Saudi security forces.

US officials had warned in recent weeks of possible attacks against foreigners in Saudi Arabia. A co-worker of Mason, Peter Carr, who left Saudi Arabia in December, said when the police guarding the foreign workers were replaced by soldiers in armoured personnel carriers, he said it was time for him to leave.

Mason, who with his wife had survived the fall of the Shah of Iran, told Carr if they got through Iran, they would get through this latest crisis.

Mason had had decided that this trip for ABB would be his last before settling down in his Booragoon home.

The 57 year old had just returned to the Arab kingdom after a three week break in Perth where he had reportedly told neighbours about his safety concerns.

A former manager of Mason described him as “one of the most positive people on earth.”

“He was a problem solver,” he said. “If you gave him a challenge he came back with solutions, not problems.”

One challenge he brought in on time and on budget was a project on Varanus Island where he was given 15 men and only 10 weeks to complete, which he did successfully.

Another Mason engineering solution of note was successfully replacing the engine on the Thevenard Island bus with an outboard engine.