A Sikh group is demanding an inquiry into the SAS’s involvement in the storming of the Golden Temple in 1984

The government has been accused of covering up the full extent of the UK’s support for India’s bloody crackdown on Sikhs in 1984.

A new report calls for a full inquiry into the role played by Margaret Thatcher’s government in the events leading up to a massacre in which hundreds, possibly thousands, of Sikhs and Indian soldiers died.

In 2014 David Cameron ordered a review after the accidental release of secret documents revealed that a British SAS officer had been drafted in to advise the Indian authorities on removing armed Sikh militants from the Golden Temple at Amritsar, Sikhism’s holiest shrine.

The documents said the plan, known as Operation Blue Star, was carried out with the full knowledge of the Thatcher government.

A report, Sacrificing Sikhs, published by the Sikh Federation UK, described Cameron’s review, conducted by Sir Jeremy Heywood, as a “whitewash”.

It claims that attempts to expose the full facts have been thwarted by government secrecy rules and conflicts of interest. More than half of the Foreign Office’s files on India from 1984 have been censored in whole or in part.

Some documents suggest the Foreign Office was aware of what was at stake when the Indian authorities approached the UK for help.

A week before the Golden Temple assault, Bruce Cleghorn, a diplomat, wrote that “it would be dangerous” for the UK government “to be identified” with “any attempt to storm the Golden Temple in Amritsar”. He was also named in correspondence discussing possible SAS assistance to India immediately after the massacre.

In 2015, Cleghorn became a Foreign Office “sensitivity reviewer” whose job involved censoring documents about the Amritsar massacre before they were released to the National Archives.

Sir John Ramsden, a member of the Advisory Council on National Records and Archives, which adjudicates on government censorship applications, was a member of the Foreign Office’s south Asia department in 1984. Ramsden wrote a letter advocating further SAS assistance for India immediately after Operation Blue Star and also argued in favour of equipping India’s paramilitary forces.

The role of the SAS officer in the days before Operation Blue Star are shrouded in secrecy as are the full extent of the fatalities. The Indian government puts the figure at about 400. Sikh groups say it was in the thousands.

According to the Sikh Federation’s report, immediately after the SAS officer carried out his reconnaissance with an Indian special forces unit, the Sikhs pulled out of peace talks believing they had seen a commando unit move into the city. The negotiations never recovered and eventually the Indian army stormed the temple in June 1984. Four months later, India’s prime minister Indira Gandhi was assassinated by one of her Sikh bodyguards, prompting reprisals that led to the deaths of more than 3,000 Sikhs.

The report suggests the UK was keen to help India because the country was one of its biggest purchasers of military equipment between 1981 and 1990. It also claims that repressive measures against Sikhs were carried out in the UK to appease the Indian government and secure arms deals.

“The government needs to finally come clean about Thatcher’s role in the Amritsar massacre and India’s crackdown on Sikhs,” said the report’s author, Phil Miller. “Whitehall censorship of historical files is like an old boys’ club that prevents the public from ever knowing how taxpayers’ money was spent. This culture of secrecy around Britain’s special forces and intelligence agencies is undemocratic and unsustainable.”

Bhai Amrik Singh, chair of the Sikh Federation (UK) said: “This report casts serious doubts on the adequacy and integrity of the inhouse Heywood review commissioned by Cameron. There has been a massive cover-up and parliament and the public have been disturbingly misled. An independent public inquiry to get to the truth is the only way forward.”