Approval has been given for work to begin on Birmingham’s new £193million civic library, amid a row over how much the project will actually cost.

City council leader Mike Whitby told the cabinet that “major and significant” reductions in the cost of providing the library had been negotiated with contractors Carillion, but refused to identify a figure claiming that the savings were bound by commercial confidentiality.

However, inquiries by the Birmingham Post revealed that just under £5 million has been shaved from the £193million estimate - less than a three per cent reduction.

The confusion arose shortly before the council cabinet gave final approval for work to begin on the Centenary Square library in January, when Coun Whitby authorised a press release announcing “significant savings” on construction costs.

No details given about how the savings had been made were released, although Coun Whitby insisted there would be no reduction in design quality.

The council also hopes to raise up to £10 million from firms willing to sponsor the new library, although backers are yet to be identified, and a further £5 million in reducing reserves for contingencies.

Coun Whitby (Con Harborne) said: “We have had very healthy negotiations with Carillion and have already made major savings in the headline price.”

Deputy Labour group leader Ian Ward challenged the council leader to identify reveal how much money would be saved.

Coun Ward (Lab Shard End) said: “I very much question what is meant by significant in this case. If you are claiming to have saved the pubic some money then you should say how much you have saved.”

The cabinet agreed to pay Carillion an, undisclosed, fixed sum to deliver the library, which is due to open in 2013.

Coun Whitby said any budget over-run would have to be met by Carillion.

Council chief executive Stephen Hughes is predicting a “substantial final underspend against the headline budget of £193 million”.

Mr Hughes said the value of the contract would be revealed as soon as final details had been agreed between the council and Carillion.

Details of the projected savings were contained in a confidential report to cabinet members.

In his press release, Coun Whitby (Con Harborne) said: “This is a major stride towards the realisation of a world-class library for Birmingham. It marks another significant chapter in Birmingham’s library story.

“The fixed lump sum we will be taking to cabinet not only guarantees the cost of the project, but also the high-quality of workmanship. In addition to this we have driven in major savings making the project even better value for money.

“By bringing together the very finest contractors, architects and library professionals in the world we are more confident than ever in our ability to deliver an iconic building which will set new standards around the world for how libraries are built and used in the 21st Century.

“It will be an iconic building to some people, although not to others. Nevertheless, it will be imposing and unforgettable.”

The library, to be built in Centenary Square between the Repertory Theatre and Baskerville House, is regarded by the council as a major flagship for the regeneration of the city which and will create 250 construction jobs including at least 25 local apprenticeships.

Connected to the Rep at ground floor and first floor levels, the new library is expected to attract up to 10,000 visitors a day, doubling the current figure of almost 5,000 per day at the existing Central Library in Paradise Forum, which is to be demolished.