THE Assembly's IT contract will cost £18m more than expected - because bosses failed to effectively estimate how many staff would use the system.

A report by the Auditor General for Wales, Sir John Bourne, released today, reveals the projected cost of the Osiris contract with Siemens Business Services now stands at £64.4m, instead of the anticipated £46.1m.

The report added that there had been so few calls to the helpdesk at evenings and weekends that each IT call effectively cost £6,000.

It said the rise in the overall cost of the seven-year contract - the first UK PFI contract for an IT infrastructure - was mainly due to the rise in user numbers.

The Assembly failed to negotiate a discount if user numbers rose. It explains that costings were based on the assumption user numbers would remain at 2,875 until April 2002 and then reduce. There are now 4,062 users.

William Graham, Conservative AM for South East Wales, said: "This is a flagrant abuse of taxpayers' money. "There's nothing wrong with the system, the problem seems to lie in the procurement of the contract. The advice taken at the time was wrong and we must look at what redress we have."

Plaid Cymru AM for Islwyn Brian Hancock added: "I am concerned that this is a repeat of the underestimation of the cost of the new Assembly building."

Ed Townsend, the Liberal Democrats' prospective Assembly candidate for Newport East, said he thought the key issue was the £6,000 cost per call to the out-of- hours helpdesk. The report concluded although the Osiris system performed well, there was limited control of expenditure because there is poor accountability for decisions that affect its budget - such as recruitment.

An Assembly spokeswoman said: "It's our practice not to issue a Press release or comment on the report, as this could be perceived as pre-empting its consideration by Audit Committee in December and the Assembly Government's response to the Audit Committee's findings and recommendations when issued.

"We welcome, in general, the value-for-money work undertaken by the AGW and the contribution it makes to helping the Assembly achieve value for money in public services, confirm that the Assembly Audit Committee will be considering and taking evidence on the Report before the Christmas recess, and that the Assembly Government will give careful consideration to the committee's recommendations."