A Sikh being held in India should be immediately released, a UN human rights group has said, after it found his continued imprisonment had no legal basis.

Jagtar Singh Johal, of Dumbarton, was arrested on November 4 2017 after travelling to the Punjab for his wedding, with local media linking his detention to the killing of Hindu leaders in the area. He is yet to stand trial.

The United Nations Working Group on Arbitrary Detention said the “continued pre-trial detention of Mr Johal lacks legal basis and is arbitrary”.

In their report, the authors said he was abducted by 15 plainclothes police officers who placed a hood over his head and pulled him into an unmarked car.

“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,” the 17-page report said.

It added there was “no judicially admissible evidence against Mr Johal, despite intelligence agencies having over three years to investigate” and the “appropriate remedy would be to release Mr Johal immediately”.

Gurpreet Singh Johal, his brother, said his family was “dreaming of the moment” he was reunited with them.

“We’ve known from the start that there’s no good reason for Jagtar’s imprisonment and in four years the Indian authorities haven’t produced any evidence against him,” he said.

“The UK Government hasn’t listened to us, but perhaps it will listen to the UN and call for his release.

“There have been so many setbacks but on a day like this we’re dreaming of the moment my brother steps off a plane in Scotland to be reunited with his family.”

During his time in detention he has been interrogated and tortured, the UN panel said, “including using electric shocks, forcing his limbs into painful positions and depriving him of sleep”.

“Mr Johal was 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,” the report said.

“The admission into evidence of a statement allegedly obtained through torture or ill-treatment renders the entire proceedings unfair, regardless of whether other evidence were available to support the verdict.

“The burden of proof rests on the Government (of India) to prove that statements were given freely, which it has not done so in this case.”

Maya Foa, director of Reprieve, described the report’s publication as a “watershed moment”.

“There is no longer any excuse for the Government’s continued failure to call for Jagtar’s release and return,” she said.

“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?”

Charlie Loudon, international legal adviser at Redress, said: “The UK Government promised ‘extreme action’ in Jagtar’s case in 2017, but has failed to live up to this commitment.

“Now that a panel of UN experts has called for Jagtar’s release, it is imperative that the UK Government does the same.”

A spokesman for the Foreign and Commonwealth Office said: “We have consistently raised our concerns about Mr Johal’s case with the government of India, including his allegations of torture and mistreatment and his right to a fair trial.

“The Prime Minister raised the case with his Indian counterpart Narendra Modi when they met in Delhi on April 22.”