The PSNI chief constable has been named among the favourites to succeed Met Police Commissioner Cressida Dick, according to reports.
She dramatically quit the role on Thursday night, just hours after saying she had "absolutely no intention" of standing down.
London Mayor Sadiq Khan said he was "not satisfied" Dame Cressida could "root out the racism, sexism, homophobia, bullying, discrimination and misogyny that still exist" in the force or restore Londoners' trust.
It is understood Mr Khan informed Dame Cressida, who became the first woman to head the Met Police in 2017, that she had lost his confidence and she resigned instead of attending a showdown meeting with him at around 4.30pm on Thursday.
Mr Khan said the final straw was the police watchdog's report into 14 cops who joked about rape, LGBT people and violence towards women in Whatsapp messages, saying he was "shocked" and "the response from the Commissioner wasn't up to the scale of the change required in the Met Police Service".
Dame Cressida's departure comes after Scotland Yard has been rocked by multiple scandals in recent months, including the force's handling of partygate, Sarah Everard's murder and repeated claims of a culture of misogyny and racism.
It has been agreed that she will continue to serve for a short period to enable an orderly handover.
According to media reports, among her possible successors is Simon Byrne, who has been PSNI chief constable since May 2019.
He replaced George Hamilton and became the fifth chief constable in the PSNI's history.
He has more than three decades of policing experience, also serving the Metropolitan Police, Merseyside, Greater Manchester and Cheshire.
Mr Byrne was chief of Cheshire Police from 2014-2017.
He was suspended over unfounded allegations of bullying but later cleared of 74 misconduct claims.
His tenure at the top of the PSNI has been marked by a number of setbacks including the handling of the Black Lives Matter protests and the Bobby Storey funeral in June 2020.
Mr Byrne was previously floated as a possible successor to Cressida Dick last September when there was growing opposition around her likely reappointment as Metropolitan Police commissioner when her contract came up for renewal in April.
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