A whistleblower who alleged abuse of inmates at Wakefield prison has been awarded compensation of £477,600 after winning a claim for unfair dismissal.
Colleagues shunned Mrs Lingard after she made claims of abuse
The amount awarded to former prison officer Carol Lingard is thought to be the highest for a public sector claim.
Mrs Lingard was treated as a "grass" after reporting claims prisoners were being bullied at the high-security jail, an employment tribunal heard.
Prison Service director general Phil Wheatley has since apologised to her.
He acknowledged the organisation, the Professional Standards Unit (PSU) - established by new whistle-blowing legislation - and his deputy all failed to deal properly with her allegations.
Mrs Lingard's claims centred on one prison officer, who she claimed had warned a sex offender he could get slashed by other inmates if he was found with images of children.
She alleged the officer then attempted to have the material planted in the prisoner's cell.
Mrs Lingard alleged the officer had forged another prisoner's records to show poor behaviour and that he was involved in a suspicious assault allegation against the same inmate.
An initial investigation - later described as "poor" and "not professional" by the tribunal - found "no evidence" to support her allegations.
Despite approaching John Slater, the prison governor, and the PSU - which briefly investigated her claims - her complaint went no further.
A Prison Service spokesman said on Wednesday: "The service acknowledges that it took an inordinately long time for the information which Mrs Lingard reported to be investigated and the investigations carried out were inadequate."
It accepted the tribunal's recommendation there should be a comprehensive review of the PSU.
Mrs Lingard said: "I remain deeply disappointed that despite giving the prison service many opportunities to take responsibility for their actions during the last three years, I have had to fight a very long and hard case at tribunal for this to happen.
"I am happy with the award and I am relieved that I can finally begin to put all of this behind me and look to the future."
Her solicitor John Sturzaker said Mrs Lingard was a "respected officer" who had highlighted "serious wrongdoings".
"Her concerns and complaints were mishandled appallingly and she felt she had to resign her post," he said.
"Mrs Lingard has now been completely vindicated by the tribunal."