A motorist who crashed exiting the M4, killing a friend, told police "something flashed" across his path causing him to lose control.

Imran Hussain said he turned off the motorway eastbound at the junction 17 Chippenham turn-off after being instructed by the voice of Darth Vader over his sat nav.

Bristol Crown Court has heard he slammed the Peugeot 307 courtesy car into a barrier and rolled down the grass verge on to the hard shoulder, leaving rear seat passenger Sean Skipp with fatal injuries.

Hussain, 26, of Oxford Place, Easton, denies causing death by dangerous driving in November last year.

Robin Shellard, prosecuting, has said it was the prosecution's case that Hussain failed to react to motorway signs and left it too late to exit safely, causing him to a lose control.

He told the court Sean was living in Bristol and knew Hussain.

When Sean's brother Jamie asked for a lift, Sean arranged for Hussain to drive, Mr Shellard said.

The court heard they set off around noon, with Jamie in the front passenger seat and Sean in the back.

After travelling up the M32 they headed east on the M4, Mr Shellard said, with Jamie expecting to get off the motorway at Bath.

He said: "The car didn't get off at Bath. Mr Hussain had a sat nav and it showed a moving image and spoke to you. The sat nav told him to come off at junction 17."

The jury heard Jamie was using his mobile when they approached junction 17 and he noticed a car to their left which prevented their exit.

Mr Shellard said: "The next thing that he knew was that the Peugeot swerved to the left. They hit something like a hole in the road – the prosecution say a drain – the car span, hit the barrier and rolled down the grass verge. Unfortunately, as a result, his brother died."

When interviewed Hussain, who injured himself in the smash, told police two lorries were to his left as he approached the junction.

He told police: "I slowed down, I indicated to come off and I slowed down and indicated again.

"As I tried to come off on the slip road something flashed in front of me. That's when I lost control."

Lorry driver Graham Baraclough told the jury he was driving his Mercedes truck and a lorry was overtaking him, when he saw a car in front turn 45 degrees towards the exit. He said: "The back end (of the car) started to go from one side to the other and it went straight back towards the motorway, hitting the crash barrier on the slip road."

The case continues.