Isambard Kingdom Brunel’s 1864 structure still has 99% of its original ironwork but needs preserving and sprucing up

It is a bit like that awkward job of painting behind a radiator – but on a vast scale and while perched high above a river gorge atop gently swaying scaffolding.

The challenging task of preserving and sprucing up Clifton Suspension Bridge’s wrought-iron chains, which needs to be done every 25 years, is in full swing.

“It’s certainly quite a project,” said Trish Johnson, the holder of the historic title of bridgemaster, who came up with the radiator comparison. “But the bridge is such an iconic structure, such a symbol of Bristol, and we can’t wait to see it sparkling again – it’s going to look great.”

The Guardian was given a rare chance this week to clamber up the scaffolding set up around the 4,200 chains; it is light and flexible and moves with the bridge’s structure in the wind.