The police investigation into allegations of perjury in the Tommy Sheridan defamation action has cost more than £1m, with an average of 14 police officers committed to it for more than a year.

Information released by Lothian and Borders Police shows much of the bill is taken up by roughly 40,000 hours of police officers' time, which is not accounted for separately, though it is reckoned to cost an average £25 per hour. A specific budget for the Sheridan investigation has run to £153,746, including overtime and expenses.

The information was obtained under the Freedom of Information Act by Hugh Kerr, one of the former Solidarity MSP's close aides. The Edinburgh-based force told him 40,000 staff hours is an "extremely approximate" estimate, as officers can be working on different cases and were drawn into the inquiry temporarily, at times when it became busier.

But even the estimate has fuelled anger in the left-wing Solidarity party, with claims its leader has been the subject of a disproportionate police effort.

Mr Kerr claims that during time spent with Mr Sheridan when he was being questioned in December, he saw 12 police officers were handling the case at the station while another nine were searching his home in Glasgow.

The case arose from Mr Sheridan's victory in a defamation case he brought against the News of the World, which had published allegations that he visited a Manchester sex club and took part in orgies. A Court of Session jury awarded the then MSP £200,000.

Sixteen months later, he was charged with perjury over his evidence. Six others who appeared in the witness stand in summer 2006 have also been charged with perjury, including his wife, Gail, his father-in-law, and former Solidarity MSP Rosemary Byrne.

His wife is being pursued over a further allegation that she stole property from her employer, British Airways, with evidence gathered during the police search of their Glasgow home in pursuit of perjury evidence. Mr Sheridan said on radio this weekend police had taken away miniatures of alcohol. He also said last week he was "disgusted, dismayed and disenchanted" at the police, accusing them of a vendetta and harassment.

"As a Lothians council tax payer I am appalled at the huge waste of taxpayers' money on this police vendetta," Mr Kerr said."

A spokesman for Lothian and Borders Police had no comment to make.