If you fall asleep in a self-driving car, it will try to wake you. Then what does it do if you don't wake up?

Some manufacturers say it will be safe simply to come to a halt wherever you happen to be - even if you're in the fast lane of the motorway.

Thatcham, the motor industry's research body, wants the law to say that when more highly automated cars hit the road in 2021, they should have to pull over and find somewhere safe to stop.

Reporter: Rory Cellan-Jones. Video Journalist: Jeremy Howell.