Driving towards Wendover he was stopped at a nearby junction while a man got out of another vehicle and into the back of the BMW.
Threatening him with a knife, the man then forced the victim to drive to an unknown location before attacking him.
The unnamed man was then forced at knifepoint to continue on to Wendover to once more be attacked by possible multiple assailants at the junction of Nash Lee Lane and Nash Lee Road. The BMW was set on fire shortly afterwards.
"This was a particularly nasty incident and we urge anyone who may have witnessed any of the events to contact the police as soon as possible," said Thames Valley police Detective Constable Lucy Jarrett.
"After the car was set alight it is thought that one of the offenders left the scene on foot and another in a vehicle. It happened at lunchtime on a bank holiday and we hope that someone may have some information to help us with our inquiries."
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