Britain's government has ordered an urgent investigation into possible U.K. involvement in the deadly 1984 raid on India's Golden Temple after recently declassified documents suggested a special forces officer advised the Indians on how to proceed.

The papers, first published by the Stop Deportations blog, detailed a secret advisory mission to India by an unnamed officer from the Special Air Service, one of Britain's most elite military units.

It's not clear whether the Indians followed the officer's plan, but the allegation that Britain played a role in the raid is explosive. The storming of the Golden Temple in Amritsar was one of the most violent episodes in the Indian government's battle against Sikh separatists, and it led to massive loss of life and a breakdown in communal relations across India.