'Brunel's other bridge' has sat unused on the Cumberland Basin for 57 years

An anonymous donor has promised to contribute half of the funds needed to restore "Brunel's other bridge".

The 176-year-old Grade II-listed swing bridge in the Cumberland Basin, designed by Isambard Kingdom Brunel, was closed 57 years ago and replaced by the Plimsoll Bridge.

Charity Brunel Swivel Bridge Group aims to restore it in time for its 180th anniversary in 2029, at a cost of £2m.

Geoff Wallis, secretary of the group, said: "We are thrilled to have been promised £1m towards restoring this incredibly important bridge."

Once restored, Mr Wallis said the bridge, known locally as "Brunel's other bridge", will provide a new link between the north and south sides of the docks for walkers, runners, cyclists and wheelchair users.

Group leaders are negotiating a lease with the council so the restoration can take place in time for the target completion date of 2029.

Mr Wallis said: "It's early days for the project still, and we're talking to senior people in the council, but so far folk have been very supportive. I think we all share the vision. The problem is there are practical issues about another bridge turning across the entrance to an operational harbour."

The bridge was constructed in 1849, a few years after Brunel's SS Great Britain. For 120 years it carried a road across Brunel's Entrance Lock to Bristol City Docks, rotating on four fixed wheels driven by a hydraulic mechanism. Following its closure, the bridge was placed on Historic England's Heritage at Risk Register in 2011.

Mr Wallis added: "I'm looking forward to standing on the lock gates over there and seeing these 75 tonnes of historic structure moving silently towards me."