Two Crown Court guards have been arrested on suspicion of supplying drugs to prisoners.
Kai Brammer, 22, and Dean Nelder, 28, have been suspended from their jobs after being questioned over an alleged cannabis dealing ring, sources confirmed.
Both men worked for security firm Serco in the custody area of Harrow Crown Court, north west London.
A 20-year-old man has been questioned on suspicion of supplying the pair.
A Scotland Yard spokesman said: "On April 12, three men aged 28, 22 and 20 were arrested on suspicion of conspiracy to supply drugs, namely cannabis.
"The 28 and 22-year-olds were also arrested on suspicion of misconduct in a public office.
"They were taken to a London police station and bailed until August."
In February, Serco custody officer Alan Redmond, 25, from Deptford, south east London, was jailed for helping to smuggle drugs and mobile phones to prisoners at HMP Brixton.
Redmond, responsible for escorting defendants to and from hearings at Inner London Crown Court, would go into the cell area of the court where he had free access to the prisoners.
The drugs were then smuggled inside the prisoner's bodies and taken into HMP Brixton.