Scotland Yard could reopen 4,000 grooming gang cases in London following a Daily Express probe.

Police chiefs have been reviewing files dating back to 2010, amid fears many rapists are still roaming freely.

More than 12,000 alleged incidents were reported to the Met during the period being examined. The cases are understood to involve a broader range of offender backgrounds and include intrafamilial abuse, online exploitation and in-person offending.

The admission is hugely embarrassing for Mayor of London Sir Sadiq Khan, who previously claimed there was “no reported cases” of rape gangs operating in the Capital.

At a London Assembly committee session, he said: “My understanding from speaking to the police, and she will appreciate, I have done on a regular basis, is and I choose my words carefully for the reasons she will understand there are no reported cases and also no indication of the grooming gangs that she is concerned about in London.”

But Tory politician Susan Hall described today’s revelations as “utterly disgraceful”.

“It has been like getting blood out of a stone,” she said.

“The resistance I have encountered has been totally unacceptable and when you look at the number of cases being reviewed you have to stop and think that is 4,000 young girls raped and sexually abused and you have to think how dreadful that is.”

An audit by Met officers found around 12,000 reports. A more in-depth review found police or the Crown Prosecution took a decision to take no further action in more than 4,000 cases.

The Met focused on any case where two or more people were linked to an attack.

These have now been passed to the NCA, which is expected to announce in the coming weeks how many the force must reopen in the hope of bringing perpetrators to justice.

The same process is going on with forces across the country, but in many areas such as South Yorkshire and Greater Manchester much progress has already been made.

While many of the abusers identified elsewhere in the country are predominantly Pakistani Muslim men, the issue in London is thought to be much more complex.

A spokesman for Sir Sadiq strongly rejected any suggestion that he had sought to cover up issues related to child sexual exploitation in the capital, saying the mayor “welcomed” the reinvestigation of the cases, and had “been clear we must leave no stone unturned”.

They said: “Any individuals or grooming gangs exploiting children for sex are utterly abhorrent and the Mayor wants justice for every single victim of these horrific crimes.

“These children have not only suffered terrible abuse at the hands of the perpetrators but have been woefully let down by the authorities meant to protect them from harm.”

Sir Sadiq’s spokesman said the mayor had “led efforts to strengthen the protection of children from exploitation and harm in all its forms, including grooming gangs”, and had made “vital investment in specialist services”.

Dept Asst Commissioner Kevin Southworth, of the Met, said: “We are fully committed to engaging with the National Inquiry and the Operation Beaconport review into past cases led by the [NCA] and the National Police Chiefs’ Council (NPCC).

“We have identified those previously closed cases that meet the criteria to be considered as part of Operation Beaconport. If it is determined that any require further investigation, we will of course take that work forward to deliver justice for the victim-survivors involved.

“We would urge anyone who has – or is still – experiencing abuse of any kind to come forward. You will be listened to and supported.”

London will be one of the first places to be investigated in the grooming gangs inquiry.

Investigators will explore “the wider network of grooming gangs across London’s satellite towns and cities”.

And it will focus on the capital’s role “in the national network of grooming gangs”. They admitted there needs to be an “early investigation” because London “has the highest rate of referrals for child sexual exploitation” in the country and extensive transport links.

Despite Mr Khan’s past denials of a grooming gang crisis in London, Girl One from the notorious Oxford scandal, says her experiences in the capital mirror the exact same systematic way gangs operated in towns like Rotherham and Rochdale, and points out her own horrific first-hand experiences prove otherwise.

As a vulnerable 13-year-old, she was repeatedly transported by her abusers from Oxford and locked in rooms across the country, including homes dotted in and around the capital.

“We were taken to London,” she revealed, speaking exclusively to the Daily Express.

“I don’t think it’s possible for us to say that in the country’s largest city, there wouldn’t be a problem with grooming. If it can happen in a posh, wealthy city like Oxford, it’s definitely happening in London. And probably has been since the 90s.”

An Express/MyLondon investigation unearthed six potential grooming gang victim cases in Met Police reports read by Sadiq Khan.

Case studies highlighted in watchdog reports – uncovered by the Daily Express – describe children being plied with drugs and alcohol, raped in hotels by groups and having their lives threatened.

Sir Sadiq and Scotland Yard consistently claimed to have “no reports” of Rochdale or Rotherham-style rape gangs in the capital.