A FINGERPRINT worker who blew the whistle on colleagues, accusing them of tampering with the thumbprint at the heart of the Shirley McKie affair, is to sue the troubled Scottish Police Services Authority for forcing him out of his job.

Gary Dempster, 40, will launch a civil action against his employers after claiming he was driven out, despite being exonerated by a six-month disciplinary inquiry into his involvement in BBC Frontline Scotland's programme about the case in March 2006.

Today the Sunday Herald can also reveal that Dempster, who was based with the service in Aberdeen, has been in a relationship with McKie for 18 months.

Dempster told the documentary that colleagues had deliberately cropped and distorted the print that ended McKie's police career when she was arrested, tried and subsequently cleared of perjury in 1999 and led to David Asbury's wrongful conviction for murder.

McKie was accused of disturbing the crime scene at the Kilmarnock home of murder victim Marion Ross two years earlier.

She received a £750,000 payout from the Scottish Executive in 2006 after the mis-identification by experts at the Scottish Criminal Record Office, which is now under the wing of the Scottish Police Services Authority (SPSA).

Dempster has been on unpaid sick leave since last year after claiming his health was wrecked by the stress of the six-month disciplinary action, which claimed he brought the service into disrepute. In fact, it transpired his line manager approved the TV interview appearance.

Dempster also co-authored a report that found fingerprint experts wrongly identified McKie's print as being that found in the house.

Dempster is claiming he was forced to take sick leave under pressure from the Glasgow bureau. His legal action is backed by the Aberdeen branch of the Unison trade union and the SNP MSP Alex Neil. Chris Morran, Unison branch convener in Aberdeen, said: "Gary followed his employment guidelines to the letter. He was shown no support whatsoever, despite that support being enshrined in the workplace policy for people who whistleblow on alleged malpractices."

Neil alleged SPSA chief executive David Mulhern broke recent promises that Dempster would be fairly treated.

The MSP said: "We are in the ridiculous situation that three people who still maintain it was Shirley's fingerprint are employed by the SPSA as expert witnesses, while Gary has been victimised by the senior management for telling the truth."

In an SPSA statement issued to the Sunday Herald, Mulhern said: "Everyone has a right to confidentiality in personal matters and we take that right seriously. We have no further comment on this particular matter."

Dempster, of Stonehaven, Aberdeenshire, refused to comment.