A government study which devised plans for massive "Titan" jails was condemned as "highly misleading" by a former top Home Office official.
Professor Carol Hedderman of the Leicester University launched a remarkable attack on a high-profile report published by Justice Secretary Jack Straw, which launched a multi-billion pound prison-building programme.
Prof Hedderman accused the author, government trouble-shooter Lord Carter of Coles, of producing a study which contained "untrue and misleading" claims.
One of Lord Carter's main justifications for the Titan programme was that a larger number of serious, violent offenders was being sent to jail.
But Prof Hedderman said the most significant change in people sent to jail was actually among minor offenders.
"The increased use of custody has been affected by the sentencing of some serious offences but the biggest single change ... concerns the number and length of custodial sentences for less serious property offences and case which are too trivial to be sent to the Crown court," she said.
"Carter gives prominence to three additional factors which have contributed to the rise in the prison population. His presentation of evidence in relation to these factors is inadequate and, it is argued, highly misleading."
Prof Hedderman is a former assistant director of the Home Office's research department, where she led work on sentencing, jails and probation.
Her report for the Centre for Crime and Justice Studies (CCJS) at King's College London attacked Lord Carter's claim that government policies had led to a fall in reconvictions.
"Currently raw reconviction rates are the best available measure for assessing the impact of changes in sentencing behaviour," her report said. "These show that Carter's claim, based on modelled reconviction rates, that there have been 'reductions in reoffending', is both untrue and misleading."
