India will wage a diplomatic campaign to reclaim the Koh-i-Noor diamond and thousands of other treasures from Britain in a “reckoning” with the colonial past, the Telegraph can reveal.

Officials in New Delhi are preparing what would amount to the largest repatriation claim faced by the UK, on a scale that would dwarf Greece’s demands for the Elgin Marbles.

India’s ministerial and diplomatic staff will be mobilised to secure the return of potentially thousands of artefacts taken to Britain during the days of empire, in what one source described as a “reckoning with the past”.

It is understood that their goal is to secure the return of the Koh-i-Noor diamond, which is one of the Crown Jewels held in trust for the King.