The Arts Team, a subsidiary practice of RHWL Architects, has been forced to confirm that its refurbishment of the late-19th-century building is flagging due to 'overlooked structural problems' earlier in the project.
The historic structure was bought by the Urdang Academy, a dance school, which planned to start the academic year in its new home. However, the move will now be delayed until January to allow essential structural work to take place.
John Williams, project architect, admitted: 'At one point we were aiming to be completed by this month, but due to additional structural work needing to be done, it's more likely to be the end of December.
'Basically, the building wasn't quite as stable as we originally thought.'
The site was chosen, according to academy boss Solange Gumain, for its large open spaces with very few pillars, providing perfect areas for dancing.
She said: 'We were meant to be in by September but the builders won't be out until the end of November, so we have had to delay the moving in date until after the Christmas period.
'It has taken longer than we hoped, and we are over budget, but we will not be disclosing by how much,' she added.
The academy decided upon Finsbury Town Hall more than three years ago, with the refurbishment specifying the replacement of all floors with specialised dance floors.
The scheme will also include a dance shop and a café, and although the public has been waiting since the registry office closed to step inside the refurbished building, it will have to wait until at least 2007 to do so again.