Met policy is not to identify detainees pre-charge, but reasons media are not naming politician are more complex
The fact that a Conservative MP has been arrested on suspicion of rape and other offences and ordered to stay way from Westminster, but has not been identified, is the result of several legal and procedural factors.
The Metropolitan police have not named him because, in line with College of Policing guidance, they do not usually identify people who have been arrested before they are charged.