Rail chiefs have begun an inquiry into how the driverless locomotive, being used by Network Rail, smashed through two level crossings near Lichfield.

The train also broke through two farm crossings, reaching speeds of 60mph during the incident on Sunday morning.

Network Rail investigators are looking into the possibility that the brake was left off by the driver.

"The loco was moving over track that was downhill all the way, so it would have quickly gathered speed" - Network Rail spokesman

The train eventually reached a set of points and derailed at Alrewas, about five miles east of Lichfield.

The incident happened at about 1015 BST on Sunday on a line which was closed for track repair work.

The Class 66 loco, owned by freight company EWS, had been used to bring ballast to the site.

A Network Rail spokesman said: "The points would have prevented the loco getting on to an in-operation part of the main line, but this was obviously a serious incident, particularly as the loco passed through a number of crossings.

"The loco was moving over track that was downhill all the way, so it would have quickly gathered speed.

"We are looking into the incident with the help of EWS."

An EWS spokesperson said: "A locomotive was derailed at Alrewas following an unauthorised movement on Sunday 9 August from an engineering site.

"No injuries occurred and a full investigation into the cause of the incident is under way."