Top secret documents, released by the National Archives at Kew, in west London, show what went on behind the scenes in Whitehall and at No. 10 Downing Street

Margaret Thatcher’s government secretly considered acquiring chemical weapons amid fears that Britain had no answer to the Soviet Union’s vast chemical arsenal, according to newly released official files.

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

However, files released by the National Archives at Kew in west London 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 paper from 1984 underlined the scale of the threat with an assessment that the Russians had more than 300,000 tons of nerve agents alone.

Reliance on a nuclear response to chemical attack lacked credibility- Michael Heseltine

In contrast, the US – which was the only Nato member to possess a CW capability – had an ageing stockpile of just 31,000 tons which was not actually declared to Nato. Meanwhile, a Home Office working group calculated that a Russian CW attack by just three aircraft on Gatwick Airport would leave 16,350 dead and 29,000 injured while a similar attack on ­Southampton dockyard would kill 33,350 and leave 42,000 injured.

A note of a meeting of senior ministers and defence chiefs held on August 8, 1984 – marked “SECRET: UK EYES A” – reported a warning by Defence Secretary Michael Heseltine that the lack of an retaliatory CW capability was a “major gap” in Nato’s armoury.

“Reliance on a nuclear response to chemical attack lacked credibility,” he warned.

Foreign Secretary Geoffrey Howe said public opinion needed to be brought “gently to a better and wider perception of the imbalance between Soviet and Nato capabilities in chemical warfare, while avoiding an upsurge of alarm”.

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

“A disadvantage of such acquisition was that it might undermine the broader support which had been built up recently in public opinion for the UK’s role as a nuclear power,” the minute noted.

“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.”

Thatcher indicated that she was sympathetic to the idea, while acknowledging the time was not yet right. She suggested sounding out the Americans, who were considering modernising their CW capability.

“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.

She added that: “Public presentation of the issue should continue broadly on present lines with the aim of bringing home to people patiently the enormous imbalance in Soviet and Western capabilities in CW and the threat which this posed.”

Why shelters plans failed

Home Office officials secretly considered plans to provide homes with chemical weapons shelters amid fears of an attack by the Soviet Union – but the scheme quickly ran into difficulties.

Files released by the National Archives show that the plan foundered after experts pointed out that people would have to remain in the sealed shelters for up to 10 hours in the aftermath of a chemical attack.

“As the cubic capacity was approximately 7 cubic metres, four people could be supported in the enclosed air for only about two to three hours,” the minutes of a meeting from April 1985 noted.

It was suggested that the air supply could be extended through the use of fans and filters – but again there was a difficulty.

“It was immediately realised that finding room for them might be a problem,” the minutes noted.

Desperate for female Speaker

She was famously reluctant to treat women as being any different from men, at least politically.

But previously undisclosed papers show Margaret Thatcher was desperate to have a woman among the British speakers at the first ever conference on life sciences in Tokyo, Japan in March 1984.

According to files released by the National Archives in Kew, west London, high-level discussions took place about who would be sent.

In a letter on December 8, 1983, the government’s chief scientific adviser, Sir Robin Nicholson, suggested that Bernard Williams, a scholar and philosopher who was provost of King’s College, Cambridge, could be a suitable alternative for the philosopher and educationalist Mary Warnock, who was unavailable.

But the then-Prime Minister dismissed the idea, writing on the memo: “No – he did a dreadful report for the Home Office some time ago. We need a lady to substitute for Mrs Warnock.”

Thatcher reiterated her support for having a woman among the speakers a year later, when discussions were being had about who should go to the second life sciences conference, to be hosted by France in April 1985.

Secretary of the Cabinet Sir Robert Armstrong proposed two speakers from the Tokyo conference – Cambridge scientist Dr Sydney Brenner and philosopher Sir Stuart Hampshire – along with Sir Robin himself.

But Mrs Thatcher again showed her desire for having representation from the fairer sex, writing: “Have we no distinguished ladies who could go – Lady Warnock herself?” Unfortunately Lady Warnock was again unavailable.