Grimshaw's eagerly awaited Bath Spa scheme has run into costly delays, sparking recriminations between the design team and contractor.
The project, which was originally due to be completed last autumn, is now six months overdue, at an estimated cost of £30,000 a week.
Main contractor Mowlem, facing charges of responsibility from the Conservative group on the council and rumours of legal action, has hit out at Grimshaw, blaming the design specification.
A statement issued by Mowlem's regional director Chris Pape claims delays were the result of 'inconsistencies and lack of detail in the project's design specifications'. It also blames Bath and North East Somerset council for shortcomings in their management of the project.
'We could point to any number of instances where this has led to significant delay, ' he said.
However, the project team, in its own public statement, denied Grimshaw was to blame and said it 'strongly refuted' suggestions that bad project management had contributed to the problems. It stressed that 'the completion date and programme are within the control of the contractor'.
The project, costed at £19 million in 2000 but now set at about £22 million, revives Bath's Roman Spa, restoring five listed buildings and creating a new five-storey building. But Tory councillor Les Kew, who warned over a year ago that the project was behind schedule, said completion has been delayed five times since September.
John Everett, chief executive of Bath council, played down the public row and claimed that a firm completion had now been set for 31 May.
'Like any complex project of this nature, various things have contributed to the delays, ' he said. 'It is extremely unhelpful to have these sorts of contractual discussions in public. The contract allows for the proper process to analyse delays. When we've gone through that process, then we'll be able to assess responsibility.'
The leader of the council, Liberal Democrat Paul Crossly, described the figure of £30,000 a week for cost overruns as 'Tory misinformation'.
He added: 'It will be the most wonderful building opening in Europe this year. All involved can be very proud.'