The high court has thrown out the Metropolitan police’s latest attempt to sack a decorated senior black officer, with a judge branding one of its arguments “hopeless”.

The ruling was a victory for Supt Robyn Williams, who the Met dismissed and then had to reinstate when a tribunal ruled the force’s leaders had been wrong to take her job away.

Williams was dismissed in 2020 for gross misconduct, after a criminal conviction for possessing child abuse images sent to her unsolicited on a WhatsApp chat group.

That conviction led to her dismissal from the Met at a disciplinary hearing chaired by a senior Met officer, despite pleas from many in policing that Williams was a role model who should keep her job.

In June 2021, the police appeals tribunal (PAT) overturned the Met decision, saying the force had acted unfairly in dismissing her. The tribunal said a final written warning would have been a fairer outcome because this was an exceptional case.

Despite that, the Met went to the high court to insist it was correct in its decision to sack Williams, and in a judgment made public on Tuesday Britain’s biggest force lost yet another high court case – having spent tens of thousands of pounds of public money.

Mrs Justice Heather Williams dismissed the Met’s arguments. Of one claim that the officer’s conviction meant she must have been dishonest, the high court judge was withering: “The complaint that the PAT failed to treat Supt Williams’ dishonesty in advancing an untruthful defence as an aggravating factor is hopeless. The PAT said in terms in its para 39 that it took this into account as an aggravating factor.”

Supt Williams, 57, won praise for her work after the 2017 Grenfell fire, when relations between the traumatised community and the authorities were fraught. She has campaigned for more women in policing and won the Queen’s police medal during her 37-year career.

In her ruling, Mrs Justice Williams wrote: “The PAT reached the conclusion that it did, because of the unique circumstances of the conviction, the officer’s stellar career, the substantial impact she had had on enhancing the reputation of the MPS as a whole and its assessment that her dismissal would reduce confidence in the police in some of the communities in which the MPS had struggled to gain trust. This was a permissible conclusion for it to reach.”

The Met said: “We will now take time to carefully consider the judgments and any next steps.”

Janet Hills, former chair of the Metropolitan Black Police Association, said the force must now stop its pursuit of Williams and doing so was a litmus test of whether it could reform.

“There has to come a time when an organisation such as the Met has to take stock and reflect,” said Hills.

“The Met need to accept they got it wrong and address this with Williams and her family. If the new commissioner is serious about building bridges with the black community then this is where he needs to start.”

The case began in February 2018 after Williams received a WhatsApp message from her sister containing a video of a young girl being abused. The sister was outraged and wanted the culprit hunted down by police.

Williams never played the video, but a jury convicted her after the prosecution said she failed to report it because she feared doing so would get her sister into trouble.

Her sister sent the abuse video to a WhatsApp group of 17 people, one of whom reported it to police. Williams was the only one of the 17 to be put on trial.