Historic tunnels that once housed Second World War mustard gas “need to be used by the public.”

The Rhydymwyn tunnels at the former Valley Works site on Nant Alyn Road, near Mold, were opened at the weekend following a trial-run last year.

They had been used for chemical and nuclear weapons research during the Second World War.

Colin Barber, chairman of the Rhydymwyn Valley History Society, said he hoped the site would now be accessible to schools and he was looking forward to involving more young people at the historic location.

“We’ve got about 40 enquiries online already and now it’s accessible to more and more people.

“We hope to get children involved because it’s within cycling distance of schools and it’s part of their heritage.

“It’s got to be used by the public now.”

In 2016 the society ran a pilot project to open the tunnels and more than 300 people were taken on managed access visits.

The venture, mainly funded by Subterranea Britannica and Flintshire Local Voluntary Council, was considered by the Department for Environment, Food and Rural Affairs (DEFRA) to be highly successful.

Among those attending the opening at the weekend was centenarian Caroline Bellis, who worked in the tunnels in 1944.

PC Fred White worked on the security at the site during the war and his son Vernon White, 82, was at the official opening.

“I can remember when they used to take the tankers full of mustard gas up to Northop,” said Mr White.

“They used to take it to a place we called Sleepy Valley, but its real name is Woodside.

“I remember the silvery, whitish tankers going up to Sleepy Valley. They had police cars to escort them, but we didn’t know when they were coming. I was only 12 at the time and didn’t pay that much attention.

“There was a German plane that dropped a bomb near there on a Saturday night.

“They reckon that if a bomb had caught one of these tanks, the whole of Flintshire would have gone up.”

The Valley Works acquired its name in 1939 when the Ministry of Supply instructed ICI’s Special Products Division to construct a factory and storage area in the Alyn Valley close to Rhydymwyn on the site of the former Bryn Celyn lead and zinc mine. The Valley Works has not been used since the mid-1990s.

In September 2008, the Runcol Building and three Pyro buildings were made Grade II Listed Buildings and 21 buildings in the danger area, including the tunnels, were designated as Ancient Scheduled Monuments by Cadw.