The Home Office does not issue guidance on internal police policy; this is a matter for chief officers and their police authorities.
However, the general practice is for police officers working in a multi-agency team who have concerns about work practices or the conduct of colleagues within the team, to raise these concerns through their usual management channels or with their Professional Standards Department, which they may contact through a confidential line if necessary.
If police officers suspect a fellow officer of acting in a way that could result in disciplinary or criminal proceedings, and feels unable to raise these concerns through usual procedures, they may raise their concerns within their force or directly to the Independent Police Complaints Commission, using their dedicated report line.