Police are investigating three train robberies across south London which they believe to be linked. 

On Tuesday April 9 a 52-year-old man who was on a train from London Bridge was approached by another man. 

He told the victim he was carrying a knife and demanded his mobile phone. 

The victim handed over his phone before attempting to get it back off him, at which point the man hit the victim repeatedly in the head and ran off the train. 

The following day at around 3.10pm a 72-year-old man was on a train waiting at the platform at London Bridge when a man approached him and snatched his phone. 

The victim tried to grab the phone back but the man threatened to stab him. 

The suspect then ran down the carriage and off the train. 

Then on Thursday, April 11, at around the same time a 25-year-old woman was travelling from Honor Oak Park to Clapham Junction station when she was approached by a man who was walking along the carriages. 

The man asked her for the time before demanding her phone and threatening to stab her. 

He then demanded she hand over her Apple Airpods and case before leaving the train at Crystal Palace station. 

British Transport Police (BTP) detective believe the three incidents are connected. 

They have released an image of a man they believe has information which could help their investigation. 

Anyone who recognises them is asked to contact BTP by texting 61016, or by calling 0800 40 50 40 quoting reference 504 of 11 April. 

Information can also be given anonymously to Crimestoppers on 0800 555 111.