A Greater Anglia train travelled at 80mph with one of its doors open for more than 20 minutes due to loose screws, accident investigators have found.

A probe was launched by Greater Anglia and government safety staff after a passenger train travelled through Essex on August 22, covering 16 miles with one of its doors open before a passenger alerted the driver.

The incident happened on one of the refurbished electric suburban trains that are used on services across Essex and up to Ipswich.

Read more: Greater Anglia train travelled with door open on service through EssexInvestigators found the door interlock system - designed to detect if any doors are not fully closed - failed because two door bracket screws had become loose and fallen out.

This meant the train was able to move away when commanded by the driver.

A Rail Accident Investigation Board (RAIB) report said Greater Anglia had since found loose screws on "at least 60 doorways" in its fleet of refurbished class 321 carriages.

Manuel Cortes, general secretary of the Transport Salaried Staffs' Association (TSSA), said Greater Anglia has "serious questions" to answer following the report.

He said: "Safety on our railways must always be paramount. Passengers need to have complete confidence that they will not be put in danger whilst riding a train.

"In this instance it's blindingly obvious that something went very wrong for a door to open when the train was travelling at 80 mph.

"This raises serious questions about the maintenance regime and security checks being carried out on Greater Anglia trains."

A Greater Anglia spokesman said: "We apologise to customers affected by this incident.

"We take the safety of our trains and customers extremely seriously and we have cooperated fully with RAIB in their investigations as well as carrying out our own investigation.

"We have introduced new more stringent safety procedures and are committed to carrying out additional checks on our trains' doors from now on."