A grade II listed theatre shrouded in scaffolding for three years will cost at least a further £850,000 of taxpayers’ money to repair.

The Congress Theatre in Eastbourne has been hidden behind scaffolding since April 2010 when chunks of concrete started falling from the front of the building.

Three years on, the scaffolding could finally be coming downafter Eastbourne Borough Council’s cabinet agreed to set aside £850,000 for initial repairs.

But Conservative opposition councillors have condemned the huge costs and time it has taken for repairs to be made.

Council leader David Tutt said: “It is hugely exciting that we can now begin returning the Congress Theatre to her former glory and, as part of our wider plans, realise our ambitions for the Devonshire Park complex.”

After the concrete fell down, the local authority erected “crash desk” scaffolding and a “full wrap” to preserve the image of the venue. The temporary measure reportedly cost more than £2,000 a month.

The council said it used the time to draw up a list of work it needed to do. The first phase will include redesigning the upper two levels of the theatre and replacing windows and frames. Weather-resistant units and solar efficient glazing will also be installed to avoid any future corrosion.

Work is due to start by the end of the year and is expected to last for 12 months, during which time the Congress will remain open.

Philip Ede, shadow cabinet member for tourism, said: “It is unacceptable that such a prominent visitor attraction in a town dependent on tourism has been left to rot behind scaffolding for all these years because of ongoing dithering in the Lib Dem administration.

“Meanwhile the costs of repair have sky-rocketed to £850,000 and they haven’t even admitted what the total cost to taxpayers of the scaffolding has been in that time, but I do know it has been paid monthly from the outset and that the last payment was £3,000.”

The council’s plans to transform Devonshire Park includes improvements to the Winter Gardens, Devonshire Park Theatre and the International Lawn Tennis Centre.