An investigation into Staffordshire police has been launched following the London Bridge attack last month in which a terrorist killed two people before being shot dead.

The Independent Office for Police Conduct (IOPC) has begun an investigation into the force’s role in the management of the attacker, Usman Khan, following his release from prison last year after serving a term for terrorism offences.

Khan, who had been living in Stafford, was given permission to travel to London by the police and probation service.

Cambridge graduates Jack Merritt, 25, and Saskia Jones, 23, died at the scene in London Bridge after being stabbed in the chest. Three others were injured.

The pair had been helping to organise a workshop for a prison-based education project, Learning Together, at Fishmongers’ Hall near the bridge. Khan had been attending the event to celebrate the project’s fifth anniversary.

He was wearing a fake suicide vest and shot dead by police on London Bridge after being tackled by members of the public, including ex-prisoners from the conference.

A statement from the IOPC said it received a referral from Staffordshire police last week relating to the force’s contact with the convicted terrorist prior to his death.

After receiving further information it concluded that a separate independent investigation should be conducted, the IOPC said, adding it was “still in its very early stages”.

The IOPC had already begun investigating the fatal shooting of Khan by Metropolitan and City of London police officers. It said it had a duty to investigate fatal police shootings and stressed that no individual police officers were under investigation, with all involved being treated as witnesses.

IOPC director of London Sal Naseem said: “Our separate investigation into the decisions and actions of Staffordshire police has just begun and will be conducted alongside the investigation into the shooting.”

Khan was jailed in 2012 for terrorist offences for his part in an al-Qaida-inspired plot to bomb high-profile locations, including the London Stock Exchange. He was released from prison under licence for terrorist offences in December last year and ordered to wear a tag.