Robin Gloag, co-founder of Stagecoach and ex-husband of Ann Gloag, has died in a car crash after a late shift driving one of his own company's buses.

Mr Gloag, 64, who started Stagecoach with his then wife and his brother-in-law, Brian Souter, was driving back from the Highwayman Coaches yard to his Perthshire home in his car when he suddenly lost control of the vehicle and crashed into a field.

His silver Renault Laguna spun upside down and landed on its roof, trapping him underneath and partially flinging him from the vehicle.

A passing driver discovered the scene on the outskirts of Perth near Inchture, known locally as Low Carse Road, where Mr Gloag lived, and called police. The force of the crash killed him instantly. He was declared dead at the scene.

No other vehicles were involved in the smash and officers yesterday appealed for witnesses to the incident, which happened between 8pm and 9pm on Wednesday, to come forward.

Meanwhile, it emerged Mr Gloag was not due to be working that evening and had only been doing a shift to cover for one of his regular drivers who was off sick. His death follows the loss of the former couple's son Jonathan, who committed suicide in a Perthshire woodland in 1999 aged 28 after battling depression.

He had broken off contact with his father after his parents' divorce in the 1980s, which was followed by the business break-up that turned the pair into infamously bitter business rivals. Ms Gloag released a brief statement yesterday in which she said: "I'm very sorry to hear of his sudden tragic death."

Mr Gloag's family were too upset to speak as they struggled to come to terms with the news at his home yesterday.

A spokesman for Tayside Police said: "About 9pm on Wednesday we received a call regarding a vehicle road traffic accident which occurred near Bogmiln Farm, Inchture, which is known locally as Low Carse Road.

"The male driver of the silver Renault Laguna, who was travelling alone, was pronounced dead by paramedics at the scene."

Mr Gloag had only just returned to work at his business this week after a holiday in north Africa.

Three weeks ago, Mr Gloag spoke of his love of his job and his plans to carry on working "for as long as I am fit enough".