A VOTING mix-up by the Liberal Democrats has diluted the impact of the government's aim to extend tagging to ease jail overcrowding.

There were two votes, one which would have enabled electronically tagged early release to apply for the first time to prisoners on a sentence of more than four years. This vote went against the government by four votes, but only because four LibDems accidentally voted the wrong way and two were too late.

Ross Finnie, John Farquhar Munro, Jamie Stone and Alison McInnes all voted the wrong way and party leader Nicol Stephen and his parliamentary group convener Iain Smith were late.

A second vote allowed prisoners to be released into home curfew six months before their planned release date, an extension of six weeks on the present period, and this was won by 65 votes to 60.

Scots Justice Secretary Kenny MacAskill had been beaten on the issue of home detention curfew at the Justice Committee last week on the casting vote of convener Bill Aitken after Labour and the Tories united in a spoiling operation to demand a "sunset clause" on the provision, meaning it would have had to come back to MSPs next year.

The first of last night's votes was a technical procedure in the name of the Parliamentary Bureau preserving the status quo by calling for no action.

SNP and LibDem MSPs were meant to vote against it as it would prevent the extension plan but because it listed in the name of the government's parliamentary business manager, Bruce Crawford, some LibDems thought they were meant to vote in favour.

An SNP spokeswoman. "We're deeply disappointed with the LibDems. It seems they cannot get out of the habit of voting with Labour."

A LibDem spokesman said: "We will have to wait and see what advice the government receive on bringing this issue back."

Mr MacAskill had described the six-week extension to eligibility for home curfew as a "straightforward, commonsense measure" at a time when the jail population reached record levels on a weekly basis.

"High risk offenders will still be excluded," he said. "Everyone will still have to serve a quarter of their sentence. This order does not change the way in which curfews operate or how prisoners are assessed to determine suitability."

But Glasgow Tory MSP Bill Aitken said: "The SNP say that this will only affect an additional 50 prisoners. That is nonsense.

"This legislation enables them, if they so wish, to release hundreds of prisoners."