Furious passengers were left trapped inside a broken-down train for almost three hours in stifling heat.

One passenger became so irate he finally forced open the train doors and walked back to Brighton station and alerted police. Police are now investigating why representatives from Connex SouthCentral did not inform them of the situation earlier.

Officers eventually helped evacuate passengers from the train and an ambulance was called for a commuter complaining of breathing difficulties. The incident started when the 17.20 Victoria train broke down between Brighton and Preston Park on Saturday because of mechanical problems.

Things started to happen after the passenger forced the door and made his way back to Brighton station. Dave Ewart, spokesman for Connex, said he did not condone the passenger's unilateral action.

He said: "Clearly this was very dangerous because we had other other trains running and we were trying to minimise the disruption. But once one person got out of the train we had to isolate the power in Brighton station, so there was extensive disruption."

The power was switched off for more than an hour, meaning no other trains could then enter or leave the station. A spokeswoman for British Transport Police said: "It was a member of the public from the train who informed us. The railway at no point contacted us and we are looking into this to see why we weren't informed.

Mr Ewart said: "There were difficulties in moving the train because of a fault with the braking system and people were on the train for longer than we would normally expect.

Services did not return to normal until after 8pm on Saturday. The cause of the breakdown is being investigated. Danny McGahey, of Puccinos coffee kiosk, said the power failure left lots of unhappy passengers stranded at the station.

He said: "There were lots of delays and people were waiting around looking very unhappy. They all seemed quite upset about the situation."