The Welsh Assembly's top civil servant is to be questioned over delays and rising costs surrounding the construction of a new debating chamber.

Permanent Secretary Sir Jon Shortridge is expected to be asked to explain why �250,000 of taxpayers' money was spent on a legal dispute with sacked architects, the Richard Rogers Partnership.

The Cardiff Bay project is years behind schedule, millions of pounds over budget.

Members of the Audit Committee are expected to have plenty of questions ready when Sir Jon faces them on Thursday.

Close attention is likely to be paid to a legal dust-up between the assembly and the acclaimed architect Lord Rogers.

Although it lost the case, a recent report by Auditor General for Wales Sir John Bourn backed the assembly government's decision to take legal action.

The estimated costs of the building have already risen from �12m up to �47m and the project more than four years behind schedule.

Contracts expected

The update report made it clear that more delays were on the way. It said: "As time passes the date when the assembly is likely to take up occupation of the new building is further delayed."

It also said a better idea of the cost would be available when bids for the contract arrived.

The Richard Rogers Partnership served notice of adjudication on the assembly for payment of disputes invoices totalling �529,000.

The assembly took legal advice and fought the claim, then served a counter claim to recover fees paid to the firm and damages.

The move cost the assembly �267,000 in fees.

But Sir John said in light of the advice it received from the Office of the Counsel General and its solicitors, the assembly considered that it was duty bound to take action to protect the public purse.

He said: "I am satisfied the assembly took appropriate advice and was justified in taking the decision it did.

"It may be disappointing that there will be further delays until the opening of the new building, but it is a positive sign that the assembly has restructured the management arrangements for the project."

The whole project has been plagued by setbacks.

Failed expectations

The Welsh Office originally set aside �12m for the building but, in November 2000, the cost rose to �26.7m. The assembly has since estimated the final cost to be in the region of �37m-47m.

The chamber was originally expected to be completed in April 2001, but that was later put back to January 2003.

Two months ago, it was revealed that it is not now expected to be opened until September 2005.

A number of firms have been invited to tender for the contract and two will be shortlisted and asked to submit costs and design plans in January.

It is understood one of the firms invited to tender is Taylor Woodrow, backed by Lord Rogers.

First Minister Rhodri Morgan had put the project on hold but the assembly rejected his proposal to build a scaled-down building.

Lord Rogers has already been paid �2.5m in fees that were linked to the cost of the building.