It was decorated in rainbow colours in an apparent tribute to key workers during the Covid-19 crisis – but highways officials have disapproved of this bridge being repainted for fear it could cause a safety hazard.

Authorities are unsure who painted the bridge between Hollesley and Shingle Street in different colours at the end of last week. The bridge crosses a creek on the only road in and out of Shingle Street, near Bawdsey, on the Suffolk coast.

It is believed to have been painted in tribute to key workers during the coronavirus crisis, just as people have been displaying rainbow posters in windows as a sign of appreciation to the NHS.

But the highways department of Suffolk County Council has warned that painting bridges and road furniture without authorisation could present potential hazards to the environment and motorists.

Suffolk Highways said it appreciated the great level of support shown to all health staff, hospital employees and other key workers, but that metal parapets on bridges were painted specific colours for safety reasons.

Hollesley Parish Council also acknowledged the gesture was probably good-natured, but said the bridge should remain white in order to be visible to road users, particularly at night.

A spokeswoman for the highways department said: “Suffolk Highways paints the metal parapets on our bridges not only to protect them but also to increase their visibility to road users, with white being the most effective colour. The paints used are to an approved highways standard designed to provide a durable coating for many years.

“While we appreciate the great level of support and appreciation shown to our key workers, Suffolk Highways does not condone painting their bridges without authorisation.

“Working within a live carriageway is particularly dangerous and the environmental risks of paint spills is significant.”