The police watchdog is investigating a force’s handling of an alleged attack in Peterborough and its possible link with the mass stabbings on a train.
The Independent Office for Police Conduct (IOPC) said it was looking at a complaint from a man who said he was punched by someone with a knife in Fletton, in the city, on 27 September.
Cambridgeshire Police has already been reviewing its prior contact with the man suspected of stabbing people on the Doncaster to London King’s Cross train on 1 November which was stopped at Huntingdon.
Anthony Williams, 32, has appeared in court charged with 11 counts of attempted murder over the Huntingdon incident and a second stabbing in east London.
Cambridgeshire Police referred itself on Monday over the Fletton incident, the IOPC said.
The force had already said it was reviewing several incidents leading up to the train attacks.
IOPC director Emily Barry said her teams had been working closely with the force to “ensure that any complaints or conduct matters identified in its review are referred to us”.
“We will keep the complainant and the force updated as our investigation progresses,” she added.
Ricky Butcher, 35, has already told the he was attacked and suffered serious facial injuries while waiting for a taxi outside Fletton Club with a group of people on 27 September.
Police have already confirmed they were reviewing whether the incident was connected with the train attacks.
An IOPC spokesperson said: “We understand from the complaint that police were called by a member of the public to a report of a man armed with a knife.
“Prior to the police arriving the complainant reports he was punched by the man leaving him with facial lacerations.
“Police attended and spoke with the complainant however, the suspect had left the scene before officers arrived, and no arrest was made at the time.”