Margaret Thatcher in a personal note to Indira Gandhi extended Britain’s full support in the aftermath of the 1984 Operation Bluestar to flush out Sikh militants holed up in the Golden Temple, a media report has said.

Thatcher, the then British prime minister, sent the note to her Indian counterpart Gandhi, saying Britain supported India’s unity in the face of demands for a separate Sikh homeland and that police were investigating threats against the safety of Indian diplomats here, the Guardian reported.

In what appears to be the first letter to Gandhi after the operation, sent on June 30, 1984, Thatcher wrote: “These have been anxious weeks for you, involving difficult decisions. I have followed closely your efforts to restore calm there, and I very much hope that the ‘healing touch’ for which you have called will open the way to a peaceful and prosperous future in that troubled region.” The letter is expected to further fuel the debate about Britain’s role in the operation after claims emerged that the country’s Special Air Services (SAS) commanders helped out with the military raid on orders of Thatcher, the report said.

The letter, seen by the Guardian, will form part of an investigation launched by Cabinet Secretary Jeremy Heywood on Prime Minister David Cameron’s orders to determine the British government’s involvement in the operation. Thatcher’s note, in response to two letters sent by Gandhi on June 9 and 14, appears to show that the Indian prime minister had expressed worries that Sikh “extremists” could use Britain as a base, the report said.

“I well appreciate your concern about the potential security threat posed by extremists outside India. We are determined not to allow our traditional freedoms to be abused by those who seek to use violence for political ends,” Thatcher wrote.

In an apparent reference to death threats against Gandhi which had been reported in the British media, the UK prime minister who died last year wrote: “We have made sure the police are aware of these statements and they are investigating them.” Thatcher also reassured Gandhi that British police were “devoting considerable resources” to safeguarding Indian government personnel in Britain, the report said.

A few months after the letter was sent, Gandhi was gunned down by her own Sikh bodyguards in a claimed act of revenge. Labour MP Tom Watson and Pat McFadden, in the House of Commons, had raised the issue of Britain’s role in the operation that left over 1,000 people dead, demanding full disclosure.

Watson and Lord Indarjit Singh had demanded an explanation after the documents made public indicated that an officer of Britain’s SAS was dispatched to help India plan for the raid on the Golden Temple. A “top secret and personal” letter, dated February 23, 1984, nearly four months before the raid in Amritsar, and titled “Sikh Community”, stated: “The Indian authorities recently sought British advice over a plan to remove Sikh extremists from the Golden Temple in Amritsar.

“The Foreign Secretary decided to respond favourably to the Indian request and, with the Prime Minister’s agreement, an SAD (sic) officer has visited India and drawn up a plan which has been approved by Mrs Gandhi. The Foreign Secretary believes that the Indian Government may put the plan into operation shortly,” the letter said.