Heathrow Airport has unveiled a driverless pod system designed to replace some bus services.

Called ULTra (Urban Light Transit), the UK-designed system started life as a Bristol University project.

Heathrow is currently the only adopter of the space-aged carriages.

Twenty-one of the battery powered vehicles, which can carry up to four passengers and their luggage, have been installed in the business car park at Terminal 5. More than 500,000 passengers are processed by Heathrow's newest terminal each year.

A central computer ensures that pods are distributed at each station according to passenger demand. When waiting for a passenger, the zero emission pods recharge at battery points.

Fraser Brown, Managing Director of Ultra PRT, who make the pods, said: “There’s an enormous sense of pride for all the staff who were involved in turning this science fiction dream into a reality at Heathrow and demonstrating the best of British innovation.”

The pods can travel at up to 25 miles per hour and use 50% less energy than a bus. The free service runs 22 hours a day and cost Heathrow £30m to develop.