Richard Prebble's Truth in Sentencing proposal is a poorly targeted billion-dollar justice spend-up which lacks credibility when placed alongside Act's tax policy, Labour justice spokesperson Phil Goff said.

"Richard Prebble's proposal would pour an additional $838 million into building and running prisons over a three year term of government. That is more than a year's entire Police budget," Phil Goff said.

"It is just not credible for Act to say they are going to cut $3.7 billion from government expenditure, at the same time as increasing justice spending by nearly $1 billion.

"Even if those sorts of sums were available - why would you blow it all on a low-return measure like Truth in Sentencing instead of prevention, policing, and tougher measures targeted at the hard core of repeat offenders?"

"United States studies conclude that spending just an additional US$1 million on treatment for drug offenders would reduce serious crime 15 times more effectively than lengthening prison terms."

Mr Goff rejected Mr Prebble's claims that his measure would not cost as much as the Department for Corrections estimate.

"The only way to avoid the cost is for sentences imposed to be reduced to compensate for Truth in Sentencing. In other words, instead of sentencing 6 years to serve 4, simply imposing a 4 year sentence. That's what the 'successful' and 'affordable' Truth in Sentencing policy in Victoria did - meaning prisoners do not actually spend more time behind bars.

"If this is what Mr Prebble has in mind, his policy is not only unworkable but also fundamentally dishonest," Mr Goff said.

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