Edwina Hart told AMs the adjudication was "embarrassing"

But the full judgement, released following pressure from within her own party as well as from the opposition, shows that while the architect did underestimate the costs, no substance was found to support her claim of his negligence.

Despite the minister's insistence that she was vindicated, the opposition parties are now calling for her to reconsider her position.

Ms Hart has admitted the matter is embarrassing, but insists the decision to sack him was right.

The adjudicator's ruling shows that the assembly was criticised for suggesting that the architects had got their figures wrong.

The assembly administration had argued that the original estimates for the new chamber, made back in 1998, were too low and on this count the Richard Rogers Partnership was found guilty.

Lord Rogers complained over unpaid fees

But this was not found to be in any way deliberate or negligent, and the architects did not mislead the assembly to win the contract.

Indeed, at various stages, increases in costs were brought to the assembly's attention and were accepted.

It has emerged that the adjudicator was concerned about the use of such a blunt accusation against the Richard Rogers Partnership.

He also criticised the way the assembly had compared the original estimates with the actual costs - which could only have been known much later.

He concluded that the architects did show reasonable skill, care and diligence.

Lord Rogers had accused Ms Hart of being unfair and inaccurate when speaking about his involvement in the proposed new debating chamber.

Ms Hart is expected to face further questions when AMs return from their half-term break.