Attempts to clean up the 60-plus sites over the last 40 years were often botched, leaving significant amounts of the highly corrosive, persistent chemical agent in the soil. Detailed records of the chemicals stored at the sites have been lost, according to evidence uncovered by a television documentary to be screened on Thursday.
Under the Chemical Weapons Convention, which Britain has just ratified , the Government is obliged to declare sites where chemical weapons were manufactured or stored. The four production facilities were Randle in Cheshire, Nancekuke near Redruth, Sutton Oak, near St Helens and Valley in Clwyd. There were also four forward filling depots at Barnham Heath in Norfolk, Thetford, Norton Disney near Lincoln,Lords Bridge in Cambridgeshire and West Cottingwith near York.
But according to Julian Hendy, producer of the film for Yorkshire TV's "3-D" series, there are more than 60 other sites, mainly former RAF and US Air Force bases, where operational records show Mustard gas was stored and then imperfectly disposed of. Sites declared clear had yielded between 20 and 120 mustard gas bombs. One site, at Riseley in Bedfordshire, was declared "safe" by the MoD in 1988. Investigators then found contamination levels 130,000 times those considered safe, and last year the MoD admitted the site was still not clear.
The Yorkshire TV team investigated one of the sites at Duncombe Park, near Helmsley, North Yorkshire, where 12-year old Peter Turner found eight Mustard Gas canisters - four of them full - and nine Phosphorous bombs in tree stumpsd. The team visited the site, which yielded three more canisters. Laboratory tests identified substances including Dithiane and oxathiane which are believed to be from the breakdown of mustard gas.
Although chemical weapons were very rarely used in action in the Second World war, Britain and the US stockpiled huge quantities in case they were needed. In 1940-41, Britain planned to use chemical weapons to help repel any German invasion of the British Isles. More stocks were amassed in 1942-43, in case they were needed to bomb Germany, and in 1944, in case the Germans used them against the D-Day landings, as a deterrent and for retaliation. More stocks were produced after the war, against the Soviet threat, but the build-up of chemical weapons ceased from the mid-1950s, when nuclear weapons became available.
Because mustard gas, a persistent agent, is extremely corrosive, it was not loaded into bombs but kept in huge tanks at the forward filling depots.
It is understood that large stocks of mustard gas were destroyed in the 1960s and 1970s, by firing bullets at the canisters and then dousing the soil with bleach. However, the decontamination measures were often inadequate.
The documentary obtained a copy of an internal MoD document from last year about the clearance of the site at Barnham, which was highly critical of earlier attempts by the Property Services' Agency (PSA) to "clear" it. A team from RAF Wittering found 16 live mustard gas bombs, each 4.5 inches in diameter. A "second sweep" has been carried out.