A previous contract with Interserve was scrapped earlier this year when it became apparent that the project could not be delivered within the agreed £9m budget.
The plan is to convert the former council offices into serviced offices and a business club. The council chamber is still used for full council meetings every other month and the Guildhall itself is still used for events. The remainder of the space is largely empty and needs refurbishing.
In May the council decided to reduce the scope of works to the 15th century building but the revised project is still expected to cost around £14m.
The contract is now being retendered, with the aim of getting work started in January 2019.