LONDON (AP) — British authorities say the cost of repairing the tower that houses London’s famous Big Ben has doubled.

Parliamentary authorities said Friday the cost of repairing the Elizabeth Tower is now estimated to be 61 million pounds ($81 million). It was previously estimated at 29 million pounds.

Authorities say the complexity of the project and the scaffolding needed to enable workers to reach heights safely has resulted in increased costs. The last extensive conservation works took place more than 30 years ago.

The works have been controversial because Britain’s most famous timekeeper, London’s Big Ben bell, will fall silent on all but a few special occasions during the repairs.

The clock tower — also commonly called Big Ben, but formally named the Elizabeth Tower after Queen Elizabeth II — is one of London’s most-visited buildings.