Overnight work is being carried out to replace some giant components of London’s landmark Tower Bridge.

Four two metre-long nose bolts have been removed and replaced for the first time in decades as part of a series of maintenance works taking place during overnight closures.

The bolts lock in place the moving parts of the bridge, known as bascules, when it is lowered to allow traffic and pedestrians to cross the 129-year-old structure.

The work is being carried out by City Bridge Foundation, the 900-year-old charity which owns and maintains Tower Bridge and four other Thames crossings.

Paul Monaghan, assistant director of engineering for City Bridge Foundation, said: “As well as being London’s defining landmark, Tower Bridge is a key part of the capital’s transport infrastructure.

“As a bridge with moving parts, it’s inevitable that we will see wear and tear, but carrying out planned work like this avoids the need for more disruptive and costly repairs further down the line.

“Doing these kind of jobs at night means we keep London moving and minimise disruption to motorists, pedestrians and the many tourists who come to enjoy the visitor attraction.”

Around 40,000 people and 21,000 vehicles a day cross the bridge, which lifts around 900 times a year to let boats pass underneath.