The trolley, which was without brakes, rolled for more than 1,600 metres on a stretch of the Tyne and Wear Metro between Newcastle and Gateshead.

The incident happened in August 2003, but details have only just emerged.

Union leaders have now stepped up calls for a public inquiry into runaway vehicles.

The Rail Maritime and Transport union (RMT) said the latest Tyneside incident and another in which a Metro locomotive was derailed, also in August, showed the urgent need for a public investigation.

No one was injured in the runaway trolley incident, but one worker was slightly hurt in the derailment.

The trolley was similar to that which killed four men in Cumbria

The locomotive was intentionally derailed.

An HSE spokesman said: "We have received a report on the incidents on Tyneside which was supplied by Nexus.

"We are still investigating what we have classed as a dangerous occurrence and we are also keeping our Tebay team informed.

"We visited the headquarters of Nexus on Tuesday and will continue to work with the organisation."

'Public inquiry'

A spokesman for Nexus said: "We regret the incidents and have destroyed the trolley involved.

"The trolley concerned did not have brakes fitted, but all others used do have them."

Bob Crow, general secretary of the RMT, said: "It beggars belief that so many incidents are now coming to light.

"It is now imperative that a public inquiry is held."

The Nexus spokesman added: "We have been complimented on the thoroughness of our work and on the standards of our reporting process and the management systems we have in place.

"Actions have been taken to ensure that our already high standards of health and safety are adhered to and improved upon after these incidents and we are proud of our health and safety record."