SECURITY company G4S is providing a £50,000 annual service to assess mentally ill patients being treated by Gloucestershire's Mental Health 2gether NHS.
The contract is one of many to be scooped up by the security firm within the NHS, to the concern of health campaigners.
It has also won bids to carry out patient transfer services, cleaning, catering and portering services elsewhere.
G4S was criticised last year after it failed to deliver enough security guards at the London Olympics.
A spokesman from 2gether NHS Foundation Trust said: "People referred for mental health assessment while in police custody in Gloucestershire access our purpose-built Maxwell Centre, supported by specialist mental health nurses, social workers, and psychiatrists.
"In addition, a contract for specialist physical health assessment for people in custody is provided by G4S. This approach reflects our intention to ensure that appropriate specialist skills are available to provide a quality experience and outcome for people using our services."
Physical health assessments in custody at the Maxwell Centre is being reviewed.
NHS England has said it must find new ways to deliver services in future as it must plug a £30 billion funding gap by the end of the decade.
Health campaigner Caroline Malloy, of 38 Degrees Action Group in Gloucestershire, said restricting outsourcing of contracts would ease NHS funds.
"We were told we needed an 'honest conversation' about a supposed multi-billion NHS funding gap, perhaps we should be asking – is it time to end the 30 year experiment in NHS outsourcing?"
Public governor of the acute Hospitals Trust in Gloucestershire, Julius Marstrand, said: "In the light of recent revelations about alleged overcharging on government contracts by G4S, it is worth noting that G4S already has tens, if not hundreds of millions of pounds worth of NHS contracts.
"G4S recently told their investors that "internationally they are increasing their focus on healthcare", which gives them "higher gross margins" than the " mainstream vanilla services we offer'."
G4S were approached for comment but did not respond.