The Metropolitan Police officers who strip-searched a 15-year-old Black girl at a school in Hackney should be investigated for gross misconduct, Sadiq Khan has said.

The girl, known only as Child Q, has said that she “can’t go a single day without wanting to scream, shout, cry or just give up” following the ordeal, in which she was strip-searched by officers while on her period.

Three Met officers involved in the incident are being investigated for misconduct by the Independent Office for Police Misconduct (IOPC), but Mayor of London Sadiq Khan has called for the severity of the investigation to be upgraded to “gross misconduct”.

While a ruling of misconduct could result in a written warning, gross misconduct would constitute a breach of the Standards of Professional Behaviour so severe that dismissal would be justified, potentially without notice.

In an open letter sent on Thursday, Sadiq Khan has urged the IOPC to consider the findings of a safeguarding report which concluded that racism had a role to play in the officers’ decision to conduct a strip search.

Mr Khan said that “allegations of discrimination would normally be considered at the level of gross misconduct rather than misconduct” and has called on the IOPC to confirm whether it intends to consider the case as one of gross misconduct.

He said: “As mayor I have been clear that London’s police service must have the trust and confidence of the public they serve and incidents such as those experienced by Child Q not only foster distrust in the Met but actively hamper any efforts to police by consent.

“Londoners rightly expect their police service to act with the utmost integrity at all times. In instances when standards are not met, Londoners need to trust that those charged with investigating allegations involving the police leave no stone unturned. This case has understandably caused widespread concern among the public and it is important that all allegations are fully investigated, and that all relevant sources of information are taken into account.”

The Met is still reeling from the resignation of its commissioner Cressida Dick following the publication of an IOPC report that found evidence of racism, homophobia and misogyny by officers at Charing Cross Police Station.

It is understood that the recruitment of a new Met commissioner is being held-up because of a dispute between Scotland Yard and City Hall over Cressida Dick’s pay-out.

London’s police force is bracing for another blow to its reputation this month, with the publication of a report from Her Majesty’s Inspectorate of Constabulary (HMIC) expected in the next week or so.

The report was commissioned by Home Secretary Priti Patel following the findings of the Independent Panel investigation into the Daniel Morgan case, which concluded the Met was “institutionally corrupt”.

Sources have said the report will be “hard-hitting” and “damning” for the Met, and there is a suggestion it may have had a part to play in Cressida Dick’s resignation. Just days before the former Met chief stepped down, she was briefed alongside Sadiq Khan and Priti Patel on the findings of the report.

The Evening Standard reported in February that one source who had seen the report said it contains “a dozen Daily Mail front page stories” that portray the Met as a force in organisational disarray.