Friary, a former Labour councillor, was snared by a blackmailer posing as a 15-year-old girl on internet chat rooms.
Officers from Hertfordshire Police had been investigating Peter Simms, who pleaded guilty to blackmail at St Albans Crown Court and was subsequently jailed for 21 months in May last year.
They flagged Friary – a blackmail victim of Simms – to the Met's Paedophile Unit.
"Inquiries revealed that Friary was one of the individuals Simms had been in contact with," said the Yard.
"Conversations between the pair involved Friary’s attempts to make arrangements to meet the individual – believing him to be a 15-year-old girl – with the intention of committing a sexual offence."
John Friary, who has been placed on the Sex Offenders Register, was arrested on 25 January (last year) and taken to Fulham police station where he was charged with "attempting to arrange to meet a child following sexual grooming".