The man - known only as Mr XY - was recruited by the force even though he was convicted in 2002 of drugging and raping a teenage schoolgirl and inviting another man to rape her.

In 2014 detectives signed him up as a Covert Human Intelligence Source (CHIS) as they tried to smash a child sex ring operating in the west end of Newcastle upon Tyne.

Details of the case can only now be reported following the conviction of the final members of the 18 strong gang.

The group, which included one white woman, were convicted of carrying out harrowing abuse against at least 22 vulnerable girls.

Last night child protection campaigners expressed deep unease about putting a convicted paedophile on the police payroll.