Thatcher's letter to Gandhi raises question of Britain's support after Operation Blue Star

"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.”

This letter would add fuel to the fire in the House of Commons in which Labour MP Tom Watson and Pat McFadden have raised eyebrows over Britain's role in Operation Bluestar.

The letter also highlights Indira Gandhi's concern over Sikh extremists using Britain as base camp for spreading terrorism.

Thatcher also reassured Indira Gandhi that British police were “devoting considerable resources” to safeguarding Indian government personnel in Britain.

The letter would 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.