David Rodley, 30, pleaded guilty to the charges, which included sexual activity with a child and possession of Class A drugs, at Oxford Crown Court.
Rodley, of Ashcroft Avenue, Sidcup, Kent, also received an extended licence period of five years.
He was also issued with a sexual harm prevention order, which will run indefinitely.
Rodley was arrested in November following an investigation by the South East Regional Organised Crime Unit (SEROCU).
He had admitted the offences, which took place between August and November 2017, at an earlier hearing.
David Rodley pleaded guilty to:
Two counts of sexual activity with a childFour counts of sexual communication with a child
One count of attempting to meet a child following sexual grooming
One count of perverting the course of justice
One count of assault with intent to resist arrest
One count of possession of a bladed article
Four counts of possession of class A drugs (MDMA, cocaine, crack cocaine and heroin)
Three counts of attempting to cause a child to watch a sexual act
Three counts of attempting to permit indecent images of a child to be taken
The three victims were aged between 14 and 15-years-old.
When arrested on 24 November 2017, Rodley was a special constable with the Metropolitan Police based at Greenwich in London.
Random Offenders From The Database