Eventually, Susan Hall snapped. The Conservative London assembly leader had repeatedly asked Sadiq Khan about the number of rape gangs in the capital, only for the Mayor to demand she be “more specific.”

“No, you know exactly what I’m talking about,” Hall told him in an exasperated tone before Khan embarked on a monologue suggesting the city’s biggest problem was county line drug-dealing gangs.

Why Khan stonewalled questions on the issue of grooming gangs that day, only he knows.

As Hall later pointed out in subsequent media appearances, it would have been easy for him to acknowledge the issue and say it was being taken seriously.

The difference in January was that there wasn’t much external pressure to put the issue at the top of the agenda.

Beyond the odd question or motion from the local assembly Conservatives, there was very little scrutiny as to whether Britain’s largest city was blighted with the type of child sex abuse rings which have left deep scars on Northern towns like Rochdale and Rotherham.

But that all changed in dramatic fashion after an Express and MyLondon investigation unearthed public records that experts confirmed as evidence that London had grooming gangs all along.

In the aftermath of the story, the Metropolitan Police revealed that a shocking 9,000 potential cases were being reviewed and the Mayor claimed, despite his previous stonewalling, to be pushing for “transparency” and “justice” for victims.

Clips of local assembly meetings don’t tend to go viral, but the seriousness of the topic raised by Hall and the flippancy with which it was handled by Khan were seized upon by right-wing commentators.

Videos of the clash went viral and were seen by millions of people on social media.

A lesser publicised point, however, was that when Khan stonewalled Hall’s questions, he was not alone in denying the existence of grooming gangs in London.

Just a month after the clash at the assembly, the Metropolitan Police Commissioner Sir Mark Rowley had been quizzed by Lord Bailey of Paddington about whether the force was missing something when it came to organised child sexual exploitation.

“I cannot guarantee there is something out there that we have not seen,” Rowley had told the former mayoral candidate.

But in terms of the broader news agenda, neither Khan nor Rowley’s comments made a dent in the grooming gangs narrative.

Spurred by the sudden interest of the world’s wealthiest man and, at that point close confidant of President Donald Trump, Elon Musk, the Labour government was grappling with the re-emergence of a scandal many believed was confined to the past.

Calls to have a national inquiry into grooming gangs were growing amidst allegations that local efforts to hold people accountable were untrustworthy.

In June, then-Home Secretary Yvette Cooper tried to put the issue to bed by announcing a series of weighty measures on group-based child exploitation.

As well as confirming there would be a national inquiry, Cooper revealed she’d asked police forces in January “to identify cases involving grooming and child sexual exploitation allegations that had been closed with no further action” and “more than 800 cases have now been identified for formal review”. She added that she expected “that figure to rise above 1,000 in the coming weeks”.

In the wake of the Home Secretary’s statement, Hall raised the issue with Khan once again and found him to be even more definitive when asked about London cases.

“I choose my words carefully for the reasons she will understand,” he replied. “There are no reported cases and also no indication of the grooming gangs that she is concerned about in London.”

He added, significantly, that there was not a hint that any of the thousand cases identified by Cooper’s formal review came from the country’s largest police force.

“I have no indication of them being in London, but the [Met Police] understands the importance of checking for the reasons that she knows,” Khan told Hall.

In September, the Express made contact with a retired Metropolitan Police detective turned whistleblower, Jon Wedger, who claimed efforts to investigate grooming gangs in London in the mid-2000s were shut down by senior officers.

Wedger’s police notebooks and reports from the time showed substantial evidence that children were being exploited in care homes in Haringey, North London, in a pattern grimly similar to the scandals in Rochdale or Rotherham.

We also found his evidence provided to the previous grooming gangs inquiry which contained examples of numerous police operations related to organised child sexual abuse.

Wedger had never seen Khan’s clash with Susan Hall and when the Express showed him the footage, he was incensed, calling on the Mayor to resign. He was not alone in that assessment; a London survivor we tracked down was also appalled.

But the mayor wasn’t having any of it. A spokesperson for the mayor told us the suggestion that he’d not responded properly to a serious problem with grooming gangs was “false, malicious, and politically motivated”.

At the same time as this denial was being issued to the Express, our sister title MyLondon had been conducting its own investigation. The title asked every single council in a Freedom of Information request whether they’d had any grooming gang investigations: only one of the 32 boroughs, Hounslow, said they had a case.

When pressed by the journalist, the council stalled and minimised, eventually explaining the three-year police investigation related to a “single child” from the area.

To test whether this total rejection could really be true, the Express and MyLondon launched a joint investigation.

As the journalists dug into the public records, it quickly became clear that far from there being “no indication” of grooming gangs in London, there was a wealth of evidence hiding in plain sight.

Using case study examples from Metropolitan Police inspection reports and delving into the witness statements from Judge Alexis Jay’s inquiry into group-based child sexual exploitation, we found 11 potential victims of grooming gangs.

We presented the details of these cases to two experts, Rochdale whistleblower detective Maggie Oliver and care sector campaigner and author Chris Wild. Both confirmed the cases passed the threshold for being indicative of grooming gangs, with Oliver suggesting that in three instances the patterns were “typical” of the type of groups she’d investigated in Greater Manchester.

As Sadiq Khan had responded directly to every one of the four inspection reports, Oliver said his stance that there was no indication of gangs was “unbelievable”. Wild went further. “Who [or] what are they protecting?” he asked.

In their official response to the findings, neither the mayor nor the Metropolitan Police altered their public position.

However, 24 hours after they sent their reply, Sir Mark Rowley during a scheduled appearance at London Assembly, got an unusual off-topic question from Labour member of the London Assembly Len Duvall.

Suddenly, the politicians who months earlier had been unwilling to discuss the topic of group-based child sexual exploitation and voted down proposals for a London inquiry suddenly wanted to talk.

In what represented a stunning U-turn from his February remark that he “wasn’t seeing it” Rowley revealed there was a “very significant number” of cases being reviewed as part of the Home Office initiative.

The week after the Express/MyLondon investigation was published, pressure increased on City Hall and the Met. Other outlets began running stories based on the claims of political opponents, suggesting that the denials in the face of public record evidence were part of a “cover-up”.

Then, late on a Friday evening, the Express saw a letter from Sir Mark Rowley to Sir Sadiq Khan which provided an “update” on the Home Office case review.

It revealed that 9,000 cases had been identified as needing reassessment.

After we published the details, a spokesperson for the Mayor finally addressed the topic of grooming gangs to claim that “Sadiq has consistently been clear to the Met that no stone must be left unturned in pursuing justice for the victims of grooming gangs and ensuring the vile perpetrators are brought to justice”.

In a subsequent, further exclusive interview with ITV, one of the few major outlets that had not previously published anything on the scandal, Khan promised to be “completely transparent”.

Hall was outraged, telling the broadcaster that for the Mayor to “pretend as though he hasn’t ignored the plight of grooming gang survivors in London, is duplicitous and disappointing”.

In addition to claiming he was pushing for transparency, Khan started discussing the ethnicities of the victims and perpetrators as he drew comparisons with scandals in the north of England.

“In some of those northern towns, with those awful perpetrators, [they] were from one particular ethnic origin, the victims from another. Those horrific cases are not the sort of cases we’ve seen in London; they’re more complex,” he said.

Ethnicity had never been mentioned in any of Hall’s questions, nor had the Express or MyLondon articles exposing the presence of grooming gangs. But speaking publicly for the first time since the story broke, Khan had decided to introduce the issue.

It is also significant that, having quite specifically not used the term ‘grooming gangs’ in public communications for years, both the Mayor’s office and the UK’s largest police force are now claiming to have been fighting the “insidious” threat the whole time.

Quite what emerges next, however, is anyone’s guess.