Police are appealing for information after a man was punched in the head in an "unprovoked attack" on a train from Brighton to London Victoria.
British Transport Police (BTP) launched the appeal for information about the incident on the evening of April 7.
The victim was in the train toilet at around 11.30pm when he opened the door after hearing a loud bang.
He was confronted by two men, one of whom went on to assault him by punching him in the head.
The man proceeded to follow the victim off the train, assaulting him further while on the platform, and pursuing him for a short while as the victim ran away.
Investigating officer PC Michael Gosling said: “I am keen to speak to anyone who was on the service at the time and may have witnessed the incident.
"Everyone has the right to travel on the rail network without fear or intimidation.
"This was an unprovoked attack which left the victim shaken by the assault.
"He was left with swelling to the side of his face and a cut lip."
Police described the man as white, of medium build and 6ft tall.
He is believed to be in his early 20s and with short brown hair.
At the time of the incident, he was wearing a dark blue hooded top and blue jeans.
Anyone with information is urged to call BTP on 0800 40 50 40 or text 61016 using 136 30/05/2017 as a reference.
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