Three men have abseiled down the tower that houses Big Ben to repair any damage to the clock faces.
The clock faces are set in an iron frame on St Stephen's Tower, which is part of the Houses of Parliament, in central London.
The trio descend each of the four sides of the clock face at a height of around 315ft (96m).
Each clock face is 23 ft (7m) in diameter, while there are a total of 312 pieces of opal glass.
Big Ben is the nickname for the Great Bell housed within St Stephen's Tower.
Two height safety specialists abseiled on the clock faces initially.
Then specialist heritage glazer Tony McGilbert abseiled to evaluate the repairs to the fragile glass fascia panels within the clock faces.
The men wore ear defenders as the clock continued to strike as they carried out the work, which was expected to last all day.
Their equipment was attached to them to ensure it cannot fall onto the ground below.
"We have worked on a lot of historic buildings such as the Tower of London, the Houses of Parliament and Bank of England," said Terri Cliffe-Harrison, a spokeswoman for height safety specialists TaskMasters.
"It's a real privilege to be working on such another famous landmark, although that makes it all the more daunting a prospect."