A man filmed stealing a mobile phone on a train and posing for pictures with his ill-gotten fare has been cautioned and fined by police.

The incident, on the 12.09am train from Waterloo to Guildford on February 2, hit the internet after comic Matt Parker made a stand.

He was sitting near an apparently drunk girl who got off and left her bag.

When a phone inside the bag rang, Mr Parker answered, explained to the person on the phone what had happened, and said he would hand it in if she did not come back.

He was so shocked by what happened next that he filmed the events and put them on his blog.

A man, later identified as a 21-year old from Addlestone, suggested to the carriage that they steal the phone.

Mr Parker said: “Thus, I was already keeping an eye on him when he moved over and then took the phone out of the bag. I was, to say the minimum, outraged.

“So I began initially tell him to put the phone back before escalating to a full yelling-at, during which I had the presence of mind to turn my phone on and video the whole thing.

“I even asked him first if he minded me photographing him stealing the phone and he was so brazened, he held it up to pose with it.”

The man in the picture left the train at Weybridge and police have appealed for information.

A British Transport Police spokesman said: “Following an appeal for information, a number of members of the public called to provide information about the incident.

“As a result, a 21-year-old man from Addlestone, Surrey, was identified and subsequently arrested on suspicion of theft before being taken to a police station in Victoria.

“When interviewed, the man fully admitted the offence and was handed a conditional caution with three conditions: to pay the 34-year-old victim £499, to write her a letter of apology and not to commit any further offences before June 14, 2012.

“Failure to comply with any one of the conditions could result in the caution being cancelled and the man being prosecuted for theft.

“We would like to thank the members of the public who came forward and provided information about this incident, allowing us to identify and arrest the person responsible.”