The firm was due to start demolition of the 1960s town hall and library to make way for new civic offices and a library this month.
But local councillors have called for new cladding and roof designs for the building in the town on the outskirts of Bristol.
The design rethink was brought on by English Heritage and the local civic society who raised concerns over the designs of the buildings.
Bath and North East Somerset council planning committee has now deferred a decision until significant alterations are made to the the proposed buildings.
A Bath and North East Somerset Council spokesman said it was determined to deliver the scheme for Keynsham and would “urgently” consider the findings of the Development Control Committee.”