Science laboratories could soon move into the historic Camden Town Hall to help pay for its £73m refurbishment.
Work on the Grade II-listed building near King’s Cross Station is due to be finished by October.
It has been a popular venue for weddings as well as home to decades of political debate.
The council considered several options for the neoclassical building, including selling it off to a developer or using part of it for housing to help cover the costs of renovation.
It decided to lease out the two upper floors and basement to businesses that would use a separate entrance.
The council’s Town Hall project director Dan Murray said: “There has been strong interest from a variety of sectors which were targeted. These included laboratories, mixed use, co-working and general offices.”
The council plans to decide on the final tenants by the end of March.
However, Murray said it might mean the public would not be able to use the roof gardens.
The debating chamber and committee rooms have decanted to the Crowndale Centre near Euston station until the work is completed.
The council also has offices at St Pancras Square.
The Town Hall was designed by architect Albert J Thomas, who cut his teeth working for the celebrated architect Edwin Lutyens, creator of buildings including the Cenotaph and the civic centre of New Delhi.
It was finished in 1937 and boasts original features, including a marble entrance hall and grand staircase.
The cabinet agreed the “major investment in building infrastructure to ensure the long-term future of the Town Hall as the council’s main democratic and civic space” in December 2019, and work started the following year.
The council appointed Purcell as the lead architects. They are also restoring Manchester Town Hall in a £330m project.
The work includes modernising the debating chamber and committee rooms with audio visual and voting equipment, three “high quality” wedding suites, and adding more space for the registry office on the ground floor.
Murray said fixes needed for the building include “a total replacement of the roof slates; more extensive repairs to the stone facade and steel frame behind it which is rusting and causing cracking”.
Some buildings from the first half of the 20th century have fallen victim to Regent Street Disease, where the steel frame corrodes and the surrounding masonry can “burst”.
Murray said this needed attention to stop stone falling off.
He added that the building was on target to meet its £63m budget, including £50m for construction costs and a £2.4m contingency fund.
The budget has increased since initial estimates suggested the scheme could cost £44m. It is likely to take 30 years to pay back the costs through renting space out – twice the length of time originally thought.
The work will also make the building more energy-efficient and cut carbon dioxide emissions by 59 per cent.
Cllr Luisa Porritt (Lib Dem, Belsize) wanted to know how much interest there was in renting work space in the building, as “so much office space is available”.
Murray said that “King’s Cross has borne out slightly well” despite the current economic difficulties of the pandemic.
Scrutiny committee members wanted to know how the costs had increased since the initial planned £44m.
Cabinet member for finance and transformation Richard Olszewski said it “was an evolving project” as the ideas for the building changed and the council altered its plans for the four floors.
He told the scrutiny committee: “I was briefed, was always asking, ‘Does it still pay for itself?’ That was the criteria, and it does. The economics of it still stack up.”
Cllr Thomas Gardiner (Lab, Kilburn) pointed out: “It’s an investment that doesn’t bear us any fruit in income terms for 30 years, that’s a lot longer than it was envisaged.”