The suggestion is that he was poisoned, he was diagnosed with acute myeloid leukaemia, a form of blood cancer and pulmonary embolisms (blood clots) in the autopsy, however he was never diagnosed before death or had any symptoms. Many experts have said this situation is very unlikely and hence has prompted a thorough enquiry from the Chief Coroner. Overall there is mass distrust between the Sikhs and the government. There has been a catalogue of events of Khanda and his family, where the Indian government have seemingly influenced decisions here in the UK.
This is just one event from a list of events the British Government has overlooked the protection of Sikhs:
https://www.bbc.co.uk/news/uk-scotland-scotland-politics-61371846
This is 6 years and still ongoing....................