Scotland Yard is probing claims that Special Branch officers attempted to interfere with an inquiry that would have revealed an MP involved in child sex crimes.
The allegation is one of 12 new cases of alleged historical corruption relating to the investigation of paedophile activities from the 1970s to the 2000s, according to the Independent Police Complaints Commission (IPCC).
It is claimed that evidence was suppressed, investigations were halted and offences were covered up because of the involvement of MPs, VIPs and police officers.
Among the new allegations is the claim that an investigation into a paedophile ring in south-west London in the 1970s was halted prematurely by high-ranking officers.
Another alleges that evidence relating to child abuse at a youth club in the 1980s and 1990s involving politicians and council officers went missing from a London police station.
The Metropolitan Police also face accusations that paperwork and evidence relating to child sex offences involving an MP disappeared and that the politician was then released without charge.