Special Branch and senior police are accused of sinking investigations into historical child sex abuse by VIPs, MPs and officers in new corruption allegations against Scotland Yard.
The police watchdog set out 12 new cases relating to the Metropolitan Police's investigation of paedophile activities spanning four decades.
It means 29 separate claims are being assessed in a probe conducted by the force and overseen by the Independent Police Complaints Commission, while a decision has not been made on how another 18 allegations will be dealt with.
The inquiry, mainly sparked by allegations made by retired Met officers, will examine suggestions that evidence was suppressed, investigations halted and offences covered up because of the involvement of MPs, VIPs and police officers
The Met's Special Branch, which dealt with high-level policing including national security, featured in three of the latest claims. One centred on allegations about an attempt in the 1970s to interfere in an investigation that would have revealed an MP to be involved in child sex offences.
The section's officers are also said to have taken over an investigation into child sex offences committed by an MP which was then shelved.
Another claim that Special Branch covered up evidence relating to an allegation that a serving Met Police officer was involved in a paedophile ring in north London is being assessed.
It is also said that, following instructions from senior officers: a prosecution against a government official in possession of indecent images of children was not pursued; a probe into a paedophile ring in the 1970s was shut down early; police failed to investigate child sex offences involving an MP; and an MP was arrested and then released without charge after a probe into a south London paedophile ring in the 1980s.
In addition, the corruption probe will examine claims that:
:: A senior officer threatened to close an investigation into a paedophile ring in the 1980s if it uncovered evidence against VIPs
:: Paperwork and evidence disappeared, including documents relating to abuse involving an MP who was released without charge
:: An investigation into child sex abuse in central London in the 1980s was halted when it became apparent that an MP was involved
:: An MP was only charged with "specimen" counts for child sex offences, rather than more numerous or serious charges
:: Officers were threatened with the Official Secrets Act if they discussed the releasing without charge of an MP following an inquiry into a south London paedophile ring in the 1980s
It is understood the allegations relate to claims involving more than one MP.
Essex Police are also under investigation over an allegation that intelligence was provided by a witness during a separate investigation indicating that an MP was involved in child sex abuse and this was not followed up.
Scotland Yard said that since March it has referred a total of 47 allegations to the IPCC concerning historical allegations of impropriety by police officers when dealing with sexual abuse between 1970 and 2005.
A spokeswoman said: "The IPCC has decided to manage 29 of those investigations; we await a decision on the remaining 18.
"We would encourage anyone who has information or knowledge of how these historic cases were investigated to come forward and assist with the investigations."
The development comes amid questions about current inquiries linked to historical abuse.
The Daily Mail reported that an internal investigation has been launched into Operation Midland after detectives found no evidence that establishment figures were responsible for killing three boys in the 1970s and 1980s.
Last month former Tory MP Harvey Proctor, who has been questioned over the claims, insisted he was a victim of a "homosexual witch hunt".
Former prime minister Sir Edward Heath and ex-home secretary Leon Brittan, both now dead, have also been named in connection with the probe.
The complex web of inquiries took a dramatic twist last month when it emerged that an alleged cover-up of child sex allegations against Sir Edward was at the centre of a corruption probe into Wiltshire Police.
An independent inquiry established by the Government under Justice Lowell Goddard to examine historical abuse claims opened earlier this year.