Six members of a south London neighbourhood police team are under investigation over claims of criminal offences and misconduct.
Anti-corruption officers are looking into allegations against six members of a unit in Bromley in south London, the Metropolitan Police said.
The inquiry follows the arrest of a police community support officer (PCSO) on suspicion of class A drugs supply.
The Met's Directorate of Professional Standards is conducting the inquiry.
There are 22 safer neighbourhood teams in Bromley.
The PCSO, who was arrested last Tuesday, has since been suspended.
He was also arrested on suspicion of misconduct in public office and harbouring an offender.
A woman police constable, a second PCSO and a member of the public were arrested by members of the Directorate of Professional Standards.
They were held on suspicion of misconduct in a public office and attempting to pervert the course of justice.
The second male PCSO was questioned over claims he undertook police checks on people on behalf of his colleague arrested on drugs allegations.
The female police constable was arrested on suspicion of falsifying information about speeding points on behalf of her partner. This is not linked to the drug-dealing inquiry.
Three others, a male sergeant, a male police constable and a male PCSO, all in their 30s, have been formally notified they are subject to a misconduct investigation.
The PCSO has been suspended and the sergeant and constable have been placed on restricted duties. The Met said it was not a criminal inquiry.
Three other men, not Met employees, were also arrested on suspicion of conspiracy to supply class A drugs.
They have all been bailed to return to south London police stations in August.
Bromley Borough Commander Charles Griggs said: "This investigation includes matters of alleged criminality and alleged misconduct, from people simply not doing their job properly to serious criminal activity such as drugs supply.
"If found proven we will take robust action."