Protecting children from grooming gangs must come before “politics, reputations and institutional” self-preservation, Sir Sadiq Khan has been told. On Thursday, victims revealed in harrowing detail how they were kidnapped, raped and beaten by monsters operating in London.

One survivor told how an Asian described her as a “nice, young white girl” after attacking her. And the Mayor of London was told the “patterns” of abuse in the capital are “very similar” to how girls were exploited in towns such as Rotherham, Telford, Oldham and Rochdale. Milly, a survivor who was attacked by a grooming gang, told the BBC: “I was 15. I was getting passed around different men every night – sometimes 10 or 15 a month.

“They just give us drink, give us drugs. Next thing I know, I’d just be in the bedroom with one of them. Then I’d come out. Could be another one. After that, it could be another one. Sometimes it was only one. Sometimes it could be three. And then we’d just leave, really.

“I don’t remember their names really. It sounds horrible, but I just know they were [South] Asian.

“Sometimes they just said: ‘Oh, you’re a nice, young white girl.'”

Another survivor, Ruth, said: “They didn’t want anything but sex. I was low, and they gave me expensive things, so I felt wanted and then slept with them.

“It felt like I had multiple boyfriends giving me attention. They were South Asian men – they took advantage of my situation.

“It’s happening in London and those who don’t believe it need to look again.”

But Sir Sadiq is facing growing criticism over his refusal to accept that grooming gangs operate in the capital.

Shadow Home Secretary Chris Philp declared: “Sadiq Khan claimed there was no rape gang problem in London. People like Khan denying the problem is why this scandal went on for so long.”

Laila Cunningham, Reform’s candidate for mayor of London said: “What this BBC investigation lays bare is horrific.

“Girls as young as 13 being passed between men, drugged, raped, and treated as ‘the lowest rung’. That was happening in London while Sadiq Khan told us repeatedly it wasn’t.

“I always knew this was happening. I knew it from reading the transcripts of girls abused outside London in places such as Oxford.

“There was never any credible reason to believe London was somehow different. But Londoners were told grooming gangs of that type did not exist here. The Mayor said there was ‘no indication’. The police and crime commissioner repeated it.

“Now, after public pressure from tireless activists and relentless reporting by the Express, the Commissioner admits he is reviewing thousands of cases and says this has ‘always been a problem’.

“That raises a serious question: if it was always a problem, why were we told it didn’t exist? Who decided denial was safer than protecting girls?

“As mayor, my mission will be absolute. I will never overlook the sexual exploitation of girls in London. I will root out the abusers, dismantle the gangs, and expose everyone who denied, minimised or covered this up.

“I am putting the system on notice: in this city, children come before politics, reputations and institutional self-protection.”

Shadow Home Office minister Katie Lam said: “These reports are utterly horrifying. Fear of causing offence must never come before protecting children, yet too often authorities have been slow to confront hard truths for fear of being branded racist.

“These patterns of behaviour are very similar to those that we’ve seen elsewhere, yet for far too long Sadiq Khan buried his head in the sand and insisted the capital did not have a problem with rape gangs. This dangerous fiction put more vulnerable girls at risk.

“Every victim deserves justice, and the public deserves the full, difficult truth. Every perpetrator, and those who covered up these crimes, must be pursued without hesitation.”

Asked in January last year how many rape gangs London had, Sir Sadiq asked seven times for his inquisitor, Susan Hall, the Conservative leader in the London Assembly, to “clarify” what she meant.

The Mayor said: “The situation in London in relation to young people being groomed is different to other parts of the country. What we have in London is young people being groomed – to use your word, not mine – to be used in county lines.”

Following pressure from the Daily Express, the Met confirmed that it would review 9,000 cases of child sexual exploitation as a result of recommendations in a review by Baroness Casey.

A bombshell 200-page report by Baroness Louise Casey concluded crimes committed by Pakistani or Asian grooming gangs were covered up to avoid inflaming community tensions.

She accused officials of being in “denial” about the scale of the grooming gangs problem.

The report also revealed asylum seekers and foreign nationals have been involved in a “significant proportion” of live police investigations.

An entire chapter of the Casey Review was labelled “Denial” and told how public bodies used “flawed data” to dismiss claims about “Asian grooming gangs as sensationalised, biased or untrue”.

Officials feared being called racist if they spoke out against Asian or Pakistani grooming gangs, it added.

Nick Timothy, Shadow Justice Secretary, said: “Sadiq Khan claimed there were no rape gangs in London. Everyone knew that was nonsense.

“Too many times, we have seen the authorities turn a blind eye to the evidence of rape gangs, putting progressive niceties before getting justice.

“The truth is often difficult to hear.

“But we owe it to the survivors to hear their stories and put an end to this scandal. It is a stain on our politics. The rape gangs must be stopped.”

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

“Since taking office, the Mayor has led efforts to strengthen the protection of children from exploitation and harm in all its forms in London, including grooming gangs. Sadiq has driven forward long-overdue reforms in the way the Met protects children and delivered vital investment in specialist services to support child victims of sexual abuse and exploitation including a new £2.4m package of support for victims and survivors to ensure they have the care, attention and specialist support services they deserve.

“The Mayor is clear that the Met must follow the evidence wherever it leads and he will continue to ensure it does everything possible to tackle all child sexual exploitation in the capital, including grooming gangs, to build a safer London for everyone.”