Civil servants should be held to account for the “scandalous” amount of money wasted on the National Offender Management Information System (C-Nomis), a union leader has said.

Harry Fletcher, assistant general secretary of the National Association of Probation Officers, called for heads to roll after a Commons public accounts committee report described the government’s failed attempt to introduce a single computer system for the prison and probation services as “a singular example of comprehensively poor project management”.

Fletcher, a long-standing and vocal critic of the National Offender Management Service (Noms) and C-Nomis, complained that “despite it doubling in cost and running over time, no individual officials have ever been held to account.” The failure of C-Nomis “has hindered effective communication between criminal justice agencies,” he added.

The select committee report, published yesterday, details how the project’s costs – expected to be £234m by completion in January 2008 – spiralled out of control without the knowledge of the project board or the Senior Responsible Owner (SRO).

Costs and progress were not monitored for the first three years of the project, said the committee, and Noms failed to address rising costs and delays until May 2007, despite a July 2006 report from the Office of Government Commerce warning that the project was failing.

The select committee’s report said the problems might not have been so bad if “the original SRO had the experience and time to fulfil the role properly”.

The cross-party group of MPs also criticised senior managers at the Home Office for appointing an SRO with so little experience.

Edward Leigh, chairman of the committee, said he and his colleagues had “become inured to the dismal procession of government IT failures which have passed before us, but even we were surprised by the extent of the failure of C-Nomis”.

“There was not even a minimum level of competence in the planning and execution of this project,” he said.The project is a “shambles”, he added, with Noms now forced to accept a scaled-down version which, instead of providing a single system, will involve different databases holding different information about the same offender, will not be delivered till 2010, and will cost double the original estimate.

A Prison Service spokesman said: “Steps have been taken to ensure that the mistakes made are not repeated.”