The UK police watchdog will oversee an investigation into claims a force failed to adequately investigate an incident involving former MP, the late Cyril Smith.
Earlier this month a retired Greater Manchester Police (GMP) officer said he was told to stay silent in 1988 over the politician.
The unnamed officer said he found Smith in the Stockport home of a known sex offender with two teenage boys.
He alleges he was threatened with the Official Secrets Act and ordered by a senior officer to say nothing about it.
Smith, who died in 2010, was the subject of sex abuse allegations and investigations over decades during his career, first as a councillor in Rochdale and later as the town's Liberal MP.
It has also been claimed that Smith was found with material depicting child sex abuse in his car but officers were told to let him go after he made a phone call.
He was never prosecuted.
The Stockport allegation will form part of GMP's ongoing Operation Clifton criminal investigation, launched last summer, which is looking at how previous reports of child sexual abuse were handled or allegedly covered up.
So far 23 alleged victims have made complaints against Smith to GMP about his activities between 1960 and 1987 at two schools or hostels for troubled teenage boys in Rochdale - Knowl View and Cambridge House.