Margaret Thatcher’s government secretly considered stockpiling chemical weapons in the 1980s in response to the Soviet Union’s chemical arsenal, according to newly released official files.

Publicly ministers claimed that they had no plans to restore the nation’s chemical warfare (CW) capability, which had been voluntarily relinquished in the 1950s.

However files released this week show that, behind the scenes, Thatcher suggested the government could be considered “negligent” if it did not build its own chemical arsenal.

A Ministry of Defence document from 1984 estimated that the Soviets had more than 300,000 tons of nerve agents alone, while the US — the only Nato member to possess then-undeclared chemical weapons — had an ageing stockpile of 31,000 tons.

Notes from a meeting of senior ministers and defence chiefs held on August 8 reported a warning by then-defence secretary Michael Heseltine that the lack of a retaliatory CW capability was a “major gap” in Nato’s armoury.

In the discussion that followed, ministers acknowledged that any moves by the government to acquire an “independent CW capability” would create “political difficulties.”

In particular concern was expressed that such an acquisition could undermine public support for Britain’s role as a nuclear power.

“Against this, it was pointed out that public opinion might

well be appalled if it was realised that the only response which Nato could offer to a CW attack would be nuclear retaliation,” the note adds.

Thatcher said she was sympathetic to the idea, but believed that the time was not yet right.

“Summing up the discussion, the Prime Minister said that it might be argued that it was negligent of the government not to acquire a CW capability. But this was not a decision which could be addressed at this stage,” the minute noted.

Responding to the disclosure, Campaign Against Arms Trade (CAAT) representative Andrew Smith said: “Chemical weapons are deadly and immoral and they need to be abolished, not stockpiled. It is also very concerning that the government was actively considering acquiring these weapons at the same time as it was denying it in public.”