A dog-walker was seconds away from losing her life when she tumbled on to a railway track in front of an on-coming train.

The driver of the packed Bedford to Brighton commuter service told how he watched in horror as the woman slipped and fell onto the rails as he approached at 65mph.

He said: "There was nothing I could have done. She was lucky not to have been killed."

The driver, who has asked not to be named, said he was approaching the foot crossing north of Hassocks when he saw a dog running across the line at 3pm on Wednesday.

He said: "I was about 200 yards away and immediately started to apply the train brakes when another dog appeared, quickly followed by a woman who slipped on the wet wooden crossing and sprawled on to the line.

"She rolled out of the way on to the other line. Luckily for her, there was no train coming on that line but she fell very close to the conductor rail which carries 750 volts."

The driver said he wanted to warn other pedestrians to take more care when they used the foot crossing.

He said: "Railway lines are dangerous and people must respect them."