Thirteen further investigations have been launched into police corruption relating to historical child sex abuse claims, the police watchdog says.
The allegations include a claim that an investigation into a paedophile ring in the 1970s in London was closed down on instructions by high-ranking officers.
Another allegation involves claims that Special Branch interfered in an investigation involving an MP.
All relate to child sex offences from the 1970s to the 2000s, the IPCC said.
Twelve involve the Metropolitan Police and one relates to Essex Police, it added.
The investigations are to be conducted by the Metropolitan Police's professional standards department, but will be overseen by the IPCC.
The majority of the investigations stem from allegations made by retired Met Police officers.
The investigations involve allegations that:
- Evidence relating to abuse at a youth club in the 1980s and 1990s, allegedly involving politicians and council officers, went missing from a London police station
- An MP was charged with specimen child sex offences and not "more numerous or serious offences"
- Paperwork and evidence relating to child sex offences involving an MP disappeared and the MP was released without charge
- Special Branch in the 1970s interfered in an investigation that would have revealed an MP to be involved in child sex offences
- An investigation into child sex abuse in central London in the 1980s was halted when it became apparent an MP was involved
- An officer serving with the Met Police was involved in a paedophile ring in north London and that evidence was covered up by Special Branch
Three of the cases involve the Met's former Special Branch - the team that had responsibility for, among other things, personal protection for VIPs, including many politicians.
The latest investigations are in addition to 17 inquires announced earlier this year.
They all related to claims about the alleged suppressing evidence, officers hindering or halting investigations, and claims offences were covered up because of the involvement of MPs and police officers.
IPCC Commissioner Jennifer Izekor said: "We are continuing to receive further referrals from the Met and have now assessed that a further 12 require management by the IPCC in addition to one from Essex Police.
"Our investigators will now oversee these investigations and ensure they meet our robust standards."
BBC home affairs correspondent Tom Symonds said the announcement of further inquiries was a "very significant development" and that the IPCC now had an "enormous workload" to carry out.
"I think this stems very much from police officers from the past coming forward and saying 'hang on a second I've got concerns about something I saw back them when I was working'," our correspondent said.
He said the inquiries were an attempt to address the "growing number of concerns among senior officers".
Scotland Yard said that since March it had referred a total of 47 allegations to the IPCC concerning historical claims of impropriety by police officers when dealing with sex 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."
Essex Police said its professional standards department would liaise with the Met and the IPCC.