Mr Johal, a Sikh from Dumbarton, was arrested shortly after travelling to the Punjab for his wedding in November 2017. He denies being involved in a plot to assassinate Hindus.

The UN working group has now said that the “continued pre-trial detention of Mr Johal lacks legal basis, and is arbitrary”, noting in particular that there is “no judicially admissible evidence against Johal, despite intelligence agencies having over three years to investigate”, The Guardian reports.

The group’s report, which has not yet been published online, reportedly concludes that Mr Johal was “targeted because of his activities as a Sikh practitioner and supporter and because of his activism writing public posts calling for accountability for alleged actions committed against Sikhs by the authorities”.

It goes on to say that he has been “deprived of his liberty on discriminatory grounds, owing to his status as a human rights defender and based on his political activism, religious faith and opinions”.

Maya Foa, director of Reprieve, said: “This is a watershed moment. There is no longer any excuse for the government’s continued failure to call for Jagtar’s release and return. When a British citizen is tortured and held in pre-trial detention for four years, facing a potential death sentence, the prime minister’s responsibility is clear. What is Boris Johnson waiting for?”