Emma Howie was labelled a "grass" and sent grass and a wreath in the post after giving evidence in a high-profile Leeds employment tribunal which saw the Prison Service pay out almost £500,000 in compensation to whistleblower Carol Lingard.

Mrs Lingard was hounded out of a promising career when she reported rumours that one of her superiors had attempted to "fit up" a sex offender at Wakefield Prison.

Ms Howie, a married mum, had been a prison officer at Full Sutton jail near York but transferred to the Wakefield jail because of hostility towards her after her role as a witness.

The 34-year-old claimed she was blanked and ignored by staff at the Love Lane prison, despite changes that were supposed to have been brought in after Mrs Lingard's tribunal in 2005, to protect whistleblowers.

The Leeds tribunal brought against HM Prison Service by Ms Howie heard how prison officer Bob Rennison, branch secretary of the Prison Officers Association (POA), had given a copy of Ms Howie's interviews, detailing her allegations of bullying and intimidation by staff including management, to senior officer Adrian McInerney. They were confidential documents.

McInerney then disclosed the details to another third party – Carol Lingard – in a phone call and she told Ms Howie.

She rang McInerney and taped the conversation, in which he admitted Mr Rennison had given him the documents and even read extracts to her.

Investigating officer for the POA, Christopher Levitt, started inquiries into the leaked documents allegation in March 2005 but according to the tribunal panel, was "led a merry dance, both by PO Rennison and SO McInerney" so the investigation dragged on for 13 months.

The panel said both men were allowed to escape a proper inquiry and challenging questions, and neither was disciplined for the lies they told.

Rennison escaped entirely without punishment, for seriously unacceptable conduct, while Ms Howie received little support from the Prison Service.

In a reserved judgment, the tribunal concluded: "It is abundantly clear from all the detailed history of this matter that the POA, far from looking after the interests of the claimant, was hostile to her as a person who had caused substantial trouble for many of its members, who were severely criticised by the Lingard tribunal. The legitimate interests of the claimant were entirely ignored."

It also said David Thompson, Governing Governor of Wakefield Prison, "clearly took the side of PO Rennison".

It accused him of writing a "grovelling" letter to Rennison, thanking him for his co-operation.

A remedy hearing will be held on April 1 to determine compensation.