I have not been able to date this photo, but I suspect it was taken around 1926 when the original iron bridge of 1868 was being replaced by a reinforced concrete one.
Blyth and Blyth and L G Mouchel, engineers, John Angus and Sons, contractor. 1926. Reinforced concrete and steel bowstring truss bridge, 5 spans. Octagonal pairs of piers support flat deck. Pierced concrete balustraded parapet with intermediate piers supporting cast-iron lamp brackets. At centre is bronze plaque recording engineers, contractors and completion dates.