A three-day hearing of the First Tier Tribunal (Information Rights) opened with a bulk of the session being held in secret as FCO officials explained their stand that the declassification of the files posed a threat to national security and international relations with India.
"It is quite unusual that we are not allowed to be part of our own appeal," said a spokesperson for KRW Law, the human rights law firm that has undertaken the Freedom of Information (FOI) appeal on behalf of UK-based freelance journalist Phil Miller on a pro bono basis.
"Our understanding is that the BJP government of India has no objection to these files being made public. Yet, the British government continues to argue in favour of them remaining classified despite an overwhelming public interest in them," the spokesperson said.
Miller's initial FOI request was turned down by the UK Cabinet Office, a decision upheld by the UK Information Commissioner in 2015.
The appeal this week is aimed at declassifying the secret files, which Miller believes could lead to further evidence of British involvement in advising the Indian government and its forces in the military operation at the Golden Temple in Amritsar, in order to secure trade and arms deals worth billions of pounds.
In 2014, some UK government documents declassified under the 30-year rule to make such material public had revealed that British military advice was given to Indian forces prior to Operation Blue Star to flush out militants holed up in the Sikh holy shrine.
The then British prime minister David Cameron had ordered a review into this discovery, which led to a statement in Parliament declaring that Britain's role had been purely "advisory" and the Special Air Service (SAS) advice had "limited impact".
The Opposition Labour party has backed some British Sikh groups, including Sikh Federation (UK), in their call for an independent public inquiry into the exact nature of Britain's links with then prime minister Indira Gandhi's government in the lead up to the Indian paramilitary operation on the shrine in June, 1984.
Last year, Labour leader Jeremy Corbyn wrote to Prime Minister Theresa May, calling for an independent inquiry and his party has since included the issue as an election pledge in its manifesto for the June 2017 general election.