A Birmingham cabinet decision to build a split-site city library was based on deficient information and did not properly take into account financial implications and likely building costs, a highly critical inquiry has found.

In a 174-page report scrutiny committee report senior councillors are accused of rushing a decision on the library without considering the full facts.

The report raises a number of questions about the suitability of a library on two sites - with the lending and reference section at Centenary Square and an archive and family history centre at Millennium Point - which it says could prove to be more expensive and less user-friendly than a £180 million single-site library at Eastside.

The cabinet is also accused of "defying common sense" by failing to ask consultants who advised on the ditched Eastside library to examine the financial case for a split-site solution.

A central recommendation of the scrutiny inquiry is that the consultants, who said the Eastside scheme by Lord Richard Rogers represented the lowest financial contribution by the council, should be asked to examine the split-site option.

The committee found that a crucial cabinet meeting in July, which decided to go ahead with the split-site option, had a report before it which did not "provide information in a sufficiently rounded form to ensure that comparisons could be made."

The scrutiny report went on: "We have to say that our review has reinforced our original judgment. Indeed, officers have openly acknowledged that the two centre option emerged so late in the day that it was inevitable that its supporting information was well short of that available for other options.

"They did not see this as a problem. We do. The cabinet should not be taking decisions without the full facts before them."

The scrutiny report concludes that the Centenary Square site proposed for the lending and reference library, between Baskerville House and the Repertory Theatre, would only be large enough for a 24,000 sq metre building. Extending to the rear, over Cambridge Street, would involve a pedestrian bridge over the road. "This does not seem to be a realistic option at this time."

The committee report raises several issues for the cabinet which it says must be addressed before the council proceeds with the split-site scheme:

* How robust is the estimated £42 million cost of the archives and family heritage centre at Millennium Point since no specific floor plan or design is available?

* Information about the design and costings of the split-site option is not detailed enough to dispel most people's "instinctive reaction" that one building must be cheaper than two.

* What chances are there that squeezing a building in between Baskerville House and the Rep would provide the scope for making it cutting-edge or even iconic?

Contributions from members of the public to the scrutiny committee were overwhelmingly in favour of either refurbishing and extending the existing Central Library or of proceeding with the Eastside library designed by Lord Richard Rogers.