The man got into the Toyota Rav4 as it waited at traffic lights in Southampton Road, ready to turn into Port Way leading to Port Solent.

He got into the back passenger side of the car and told the 53-year-old female driver to drive. Her 18-year-old son was also in the car.

The car turned into Port Way and moments later the man fell from the vehicle on to the road.

During the fall he suffered potentially life-threatening injuries. The police have not yet released details of how he fell from the car.

An air ambulance was called and the man was rushed to Southampton General Hospital for treatment. His injuries were described as life-threatening.

He remained unconscious in hospital today and has not yet been interviewed by police.

The incident happened at 4.10pm on Saturday.

Police say a man standing on the corner of Port Way may have seen the man climb into the Toyota or fall from the vehicle and are urging him to get in touch.

PC Scott Davison, from Cosham Roads Policing Unit, said: 'I would appeal to anyone who may have seen either the man getting into the car at the traffic lights on Southampton Road, or the incident where he fell on to Port Way, to get in contact.

'In particular, any of the people in the other vehicles that may have been behind the Rav 4 and witnessed the incident should call me.'

Paul O'Shea, from Portchester, drove past the scene with his family moments after it happened and stopped to offer help.

He said: 'The guy was lying on the road without his shoes on and he was in a real state. He was barely conscious and there was blood everywhere.

'We thought he had been run over.'

Anyone with information should contact the Cosham Roads Policing Unit, quoting Operation Firtrees, on 0845 045 4545 or 01962 841534, or call Crimestoppers anonyously on 0800 555111.