Scotland Yard is facing new allegations of a cover up after it was reported that an undercover police investigation that had gathered compelling evidence of child abuse in the 1980s was scrapped shortly after detectives moved in to make arrests.

BBC Newsnight said it had been told that during a three-month secret inquiry, officers had gathered a substantial amount of evidence – including photographs and video taken from inside a London flat - of men abusing boys aged around 14 years old.

The police investigation is alleged to have led to the late Liberal MP Sir Cyril Smith being taken into a police station after officers arrived at a house in Streatham, South London, that was hosting sex parties involving teenage boys. But the programme alleges he was released within hours without any charges.

Cyril Smith (centre) was allegedly released without charge after being taken in for questioning over sex parties involving teenage boys (Rex Features)

Newsnight claims that the officers were then ordered to hand over all their evidence – including notebooks and video footage – and warned to stay quiet about the investigation or face prosecution. A desk sergeant that had wanted to keep Smith in custody overnight was reprimanded.

According to one testimony, officers were read out the Official Secrets Act to deter them from speaking out further. They were then assured that those who had been caught “would not be playing a role in public life any more”, but Smith continued as an MP until 1992. He died in 2010.

The allegations emerged shortly after the Independent Police Complaints Commission (IPCC) announced it was investigation allegations of corruption inside Scotland Yard, including claims that it covered up child sexual abuse by senior officers and MPs.

Operation Midland has already been set up to investigate child sex abuse claims at Dolphin Square (Corbis)

One of the allegations refers to Dolphin Square, an apartment block near the Houses of Parliament where sex parties involving under-age boys are claimed to have taken place. The inquiry will cover 14 referrals spanning four decades from the 1970s to 2005. The Met said it had voluntarily referred the allegations to the watchdog.

In pictures: White Flowers Campaign to support child abuse victims Show all 10 1 /10 In pictures: White Flowers Campaign to support child abuse victims In pictures: White Flowers Campaign to support child abuse victims White Flowers Campaign A campaigner holds a banner at Old Palace Yard in Westminster, during an event organised by the White Flowers Campaign Group, in commemoration of victims and survivors of child abuse In pictures: White Flowers Campaign to support child abuse victims White Flowers Campaign Pictures, messages and floral tributes left at Old Palace Yard in Westminster, organised by the WhiteFlowers Campaign Group in commemoration of victims and survivors of child abuse In pictures: White Flowers Campaign to support child abuse victims White Flowers Campaign Jenny Tomlin, the mother of Martine McCutcheon, attends a gathering at Old Palace Yard in Westminster, organised by the White Flowers Campaign Group, to lay white flowers in commemoration of victims and survivors of child abuse In pictures: White Flowers Campaign to support child abuse victims White Flowers Campaign Child abuse campaigner Bill Maloney speaks to relatives, supporters, victims and survivors of abuse as they gather at Old Palace Yard in Westminster to lay white flowers in commemoration of victims and survivors of child abuse In pictures: White Flowers Campaign to support child abuse victims White Flowers Campaign Rotherham MP Sarah Champion speaks during a gathering at Old Palace Yard in Westminster, organised by the WhiteFlowers Campaign Group, to lay white flowers in commemoration of victims and survivors of child abuse In pictures: White Flowers Campaign to support child abuse victims White Flowers Campaign Simon Danczuk MP speaks during a gathering at Old Palace Yard in Westminster, organised by the WhiteFlowers Campaign Group, to lay white flowers in commemoration of victims and survivors of child abuse In pictures: White Flowers Campaign to support child abuse victims White Flowers Campaign John Mann MP attends a gathering at Old Palace Yard in Westminster, organised by the WhiteFlowers Campaign Group, to lay white flowers in commemoration of victims and survivors of child abuse In pictures: White Flowers Campaign to support child abuse victims White Flowers Campaign A woman leaves a floral tribute at Old Palace Yard in Westminster In pictures: White Flowers Campaign to support child abuse victims White Flowers Campaign Relatives, supporters and survivors of abuse hold a minutes silence during a gathering at Old Palace Yard in Westminster, organised by the WhiteFlowers Campaign Group, in commemoration of victims and survivors of child abuse In pictures: White Flowers Campaign to support child abuse victims White Flowers Campaign Jenny Tomlin, the mother of Martine McCutcheon (left) supports Esther Grace of Cardiff, a victim and survivor of abuse, during a gathering at Old Palace Yard in Westminster, organised by the WhiteFlowers Campaign Group, to lay white flowers in commemoration of victims and survivors of child abuse

The Independent