Historic air raid shelters in Harpenden are being filled with cement following safety concerns.

A structural survey of four underground bunkers concluded they were a “catastrophic risk to public safety” under well-used pedestrian routes - there are two under Leyton Green, one by the sensory garden on Bower’s Parade, and one under Queens Road.

Work to pour aerated concrete into the shelter hatches will start today and go on for about two weeks, from Monday to Friday 8am to 5.30pm.

This technique has been chosen to do least harm to the environment.

Projects and community manager at Harpenden Town Council (HTC), Phil Wright, said: “This has been forced upon us for safety reasons and it isn’t something we would have chosen.

“The person who did the structural survey indicated that any renovations would be cost prohibited. That is to say, it would cost too much to preserve it.”

In order to save the history, HTC has created 3D scans of the underground shelters, which will be available to view online.

There will also be information boards erected at Leyton Green and Bower’s Parade about the shelters and World War Two.

A letter was sent to Harpenden residents notifying them of the work. It read: “The surveys showed that the structures have deteriorated significantly and are a catastrophic risk to public safety.”

HTC has commissioned Procare Construction to fill the shelters in.

Adding: “Procare will endeavour to minimise their impact on the local area, instructing all contractors of the importance of observing parking and access arrangements, particularly for the closest neighbours.”

According to the Harpenden and District Local History Society, excavation work on the Bower’s Parade shelter started just nine days before then-Prime Minister Neville Chamberlain declared war with Germany in 1939.

It was built in a dog-leg shape, with six 10-yard lengths connected by 90 degree corners, using reinforced concrete for the walls and roof.

There were wooden benches and chemical Elsan type toilets behind sackcloth modesty screens for the comfort of 180 people who could fit inside.

HTC has ensured the shelters are now empty before work begins.