A train which “ran away” for more than two miles before it smashed into wagons on a Mid Wales narrow gauge railway, had a brake fault, an investigation has revealed.

Two of the three people on board escaped with minor injuries but the train was badly damaged in the incident, which happened on the Welshpool and Llanfair Light Railway on March 3.

A report, released by the Rail Investigation Branch, found that the incident was caused by a brake controller being left in the “on” position and being locked in the “off” position.

At the time, the railway had been closed to the public and the train, consisting of the locomotive and one wagon was being used to take workers and equipment to a track relaying site outside Welshpool.

The driver was in the process of changing to the Llanfair end when the diesel locomotive, known as the Wasp, began to run away.

The train ran down hill for about 2 miles, reaching speeds of 30mph and passing over two open level crossings before it arrived at Welshpool Raven Square Station where it collided with five wagons.

The report said the RAIB had found that “the design of the interlock arrangement was such that it could be bypassed relatively easy”.

It added: “The braking system on the Wasp is significantly different to that of other vehicles operating on the Welshpool to Llanfair Light Railway.”

It concluded that “the underlying cause of this accident was that no formal document risk assessment was undertaken for the operation of this vehicle on the railway prior to its introduction into service, and as such possible failure mechanisms and hazards specific to the railway were not identified or considered”.