The driver of the tram involved in the devastating crash in Croydon had likely fallen into a 'microsleep' before speeding round a shart bend, an investigation has found.

Alfred Dorris, 43, from Beckenham was driving the tram when it came off the tracks at almost four times the speed limit in darkness and heavy rain on November 9 last year, killing seven people and injuring 51.

The Rail Accident Investigation Branch (RAIB) believe it is "probable" he "temporarily lost awareness" on a straight section of track and may have fallen into a “microsleep” for up to 49 seconds.

Such sleeps can last "anywhere from a fraction of a second to a few minutes" and often involve closing of eyes or head nodding, investigators said.

When he roused from his disorientation, he initially believed the tram was travelling in the opposite direction, not realising the bend was approaching.

Some passengers described the crash that followed as "like being in a washing machine", the RAIB said. People fell through the openings where windows had smashed and doors were torn off.

They were "crushed under the tram" as slid for three seconds and 27 metres before coming to a rest.

RAIB made 15 safety recommendations including operator Tram Operations Ltd, owned by FirstGroup, reviewing its management of driver fatigue, the use of tougher windows and better signage at high risk locations.

Since the accident, infra-red eye monitors have been installed in each cab on the Croydon tram network as part of a series of safety enhancements.

Tram drivers who responded to a questionnaire issued by investigators revealed that nine of them had previously used an emergency brake to comply with the 12mph limit at Sandilands junction.

Investigators found the risk posed by late braking at the location were not fully grasped by tram managers due to some drivers feeling a "reluctance" to report their own mistakes.

This was the case for the driver who did not report a "serious overspeeding incident" at the same bend just nine days before the fatal crash, in which a tram entered the bend so quickly it almost overturned.

Forensic analysis by the RAIB found that the tram involved in the derailment reached the maximum permitted speed of 50mph as it entered the first of three tunnels which stretch for 500 metres.

It should have slowed down significantly as it emerged from the tunnels on the approach to the sharp left-hand curve at Sandilands junction.

Mr Dorris did apply the brakes but the tram was still travelling at 45mph when it passed a speed limit sign, entered the corner and turned over onto its right-hand side.

He was arrested at the scene and questioned on suspicion of manslaughter and is on bail after last being interviewed by police in October. The RAIB report is separate to the criminal investigation.