Scotland Yard is probing claims that Special Branch attempted to interfere in an inquiry that would have revealed an MP was involved in child sex crimes.

The allegation is one of 12 new cases of alleged historical corruption relating to the investigation of paedophile activities dating from the 1970s and 2000s, the Independent Police Complaints Commission said.

The new claims being examined by Britain's largest force are in addition to 17 announced earlier in the year.

They involve allegations that evidence was suppressed, investigations were halted and offences were covered up because of the involvement of MPs, VIPs and police officers.

The IPCC is managing and overseeing the corruption inquiries, which are to be conducted by the Metropolitan Police's Directorate of Professional Standards.

Most of the investigations have been sparked by allegations made by retired Met officers.

Special Branch 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.

Special Branch 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 the section 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 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; an MP was arrested and then released without charge after a probe into a south London paedophile ring in the 1980s.

The corruption probe involving the Met will also 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 breaking 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.

Essex Police has also been drawn into the corruption probe 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 investigated.

IPCC Commissioner Jennifer Izekor said: "Our investigators will now oversee these investigations and ensure they meet our robust standards."

The development comes amid questions over current investigations linked to historical paedophile allegations.

An inquiry into alleged murders by VIP sex abusers was today said to be in crisis. 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 is a victim of a "homosexual witch hunt" and called for the main witness - known by the pseudonym "Nick" - to be stripped of his anonymity.

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.

In the wake of the revelation, it emerged that several forces around the country were also carrying out inquiries linked to allegations against the late politician, who died at home in Salisbury aged 89 in July 2005.

An independent inquiry established by the Government to examine historical abuse opened earlier this year.

Its chairwoman Justice Lowell Goddard vowed that the probe would travel from the "corridors of power" in Westminster to the poorest parts of the country to uncover the true scale of child sex crimes.