What is happening at Sheffield's Old Town Hall, after workers are seen entering historic building?

Three men were yesterday photographed accessing the property via a back door on Castle Green, carrying what appeared to be large wooden boards.

This morning, surveyors at the site in Castlegate said they had begun examining the building last week and expected to conclude their survey next week.

They were unable to say who they were working for but is believed at this stage that they were brought in by the owner G1 London Properties to carry out the assessment.

The latest drama comes less than a fortnight after it emerged Sheffield Council had started legal proceedings to secure the keys to the property so essential repairs could be made to the derelict building's roof.

Valerie Bayliss, chairwoman of the Friends of the Old Town Hall, this morning said she had been told only this week by the council that it expected the case to appear at court in the coming days.

She said this led her to believe the work was being done on behalf of the owners rather than the council.

"It's very odd. When the council wanted to gain entry to deal with the longstanding roof problems the owner claimed it didn't have a key," she said.

"I was told the council was going to court this week to secure permission to enter the building.

"This is a listed building and for a lot of work inside you would need consent, though there is work you can do without needing permission.

"If I were working for the council I would want to know what they're up to to ensure they're not breaching any regulations."

The Star has contacted the council and Colloco, which has been acting as the agent for the owner, but has yet to receive a response.

The council has set aside money to inspect and weatherproof the building, as part of an £800,000 fund to kick-start the regeneration of Castlegate. It said earlier this month it was taking legal action with a view to ordering urgent repairs and fitting new locks.

The Grade II-listed building, which was home to the city’s administrative HQ and courts, is still listed for sale by Colloco. But it is understood the owner is now putting together its own plans for the site’s regeneration.

The friends group, meanwhile, is seeking to buy the building for the people of Sheffield and restore it at an estimated cost of well over £10 million.

It is considering inviting people to buy community shares to help fund the purchase.