Details of his grandfather’s past have been uncovered by award-winning journalist Shyam Bhatia, who is set to publish his findings in a book.

According to the findings, Sunak’s paternal grandfather moved from the Punjab to Nairobi as a young man, was involved in schooling Mau Mau militants in guerrilla techniques.

Ramdas’s activities were carried out despite him being on the British colonial payroll.

Moreover, Ramdas, who died in 80s, is believed to have become involved in the fight for Kenyan freedom through Makhan Singh, a childhood friend from India who became a prominent trade unionist in Kenya and a sympathiser of the Mau Mau rebels.

He later moved countries again after the independence as Kenya turned unpleasant for Indians. In 1971, he headed for Britain, already home to two of his adult sons studying at university.

Ramdas helped to establish the Vedic Society Hindu Temple. He died aged 63.

The year of his death, 1980, also marked the birth of Rishi Sunak, whose father, Yashvir, followed in Ramdas’s footsteps to become a trustee of the temple.

The documentary about the temple was made last year, which showed photos of the politician-to-be enacting scenes from Hindu mythology.

Political observers say Ramdas’s links to the RSS are likely to be embarrassing for the PM, as the group was banned in India three times for its extremism.