UK intelligence agencies have been accused of tipping off Indian authorities about a Scottish man prior to his abduction and alleged torture by Punjab police.
Jagtar Singh Johal, from Dumbarton, was in India in 2017 when his family say he was forced into an unmarked car.
He says he was then tortured for days, including with electrocution, and has remained in detention since then.
Successive prime ministers have raised Johal’s case but the Indian government has denied he was mistreated or tortured.
Johal was an active blogger and campaigner for Sikh human rights, which is said to be the reason he was brought to the attention of the Indian authorities.
In May, he was formally charged with conspiracy to commit murder and being a member of a terrorist gang.
He will be presented with a full list of all the charges being brought against him next month and could face the death penalty.
The Indian authorities say the charges are related to Sikh nationalism, though Johal denies any wrongdoing.
Human rights group Reprieve has shown documentation to the BBC which says there is strong evidence Johal’s arrest came from a tip-off from British intelligence.
The UK Government has said it will not comment on an ongoing legal case.
Reprieve says it has matched several details relating to his case to a specific claim of mistreatment documented in a report by the watchdog which oversees the intelligence agencies.
A report from the Investigatory Powers Commissioner’s Office (Ipco) said: “In the course of an investigation, MI5 passed intelligence to a liaison partner via the Secret Intelligence Service (MI6).
“The subject of the intelligence was arrested by the liaison partner in their country. The individual told the British Consular’s Official that he had been tortured.”
Johal does not appear by name in the report, but Reprieve’s investigators believe the facts match his case owing to the dates concerned, the lobbying by British prime ministers and supporting evidence detailed in the Indian press.
In 2017, the Hindustan Times reported Johal had “come under the scanner” after “a source in the UK” gave the Punjab police “vague information” about a key man, “Johal”.
Speaking to the BBC, his brother Gurpreet said he was unaware of any activity that could be considered illegal.
Johal is currently being held in a Delhi prison. He has alleged that following his arrest he was held incommunicado, was interrogated for hours, and was initially denied access to a lawyer or British consular officials.
He says he was told to sign blank sheets of paper which went onto be used against him as a false confession.
On August 12, Johal lodged a claim in the High Court against the Foreign Office, the Home Office and the attorney general, alleging that UK intelligence agencies had unlawfully shared information with the Indian authorities when there was a risk he could be tortured.
Reprieve says this case suggests the Government has not fixed shortcomings surrounding its policy on torture and the death penalty, and has learned little from past failings such as the MI6 tip-off which led to the rendition and torture of Libyan dissident Abdulhakim Belhaj.
Speaking about the allegations, MP Steve Baker said: “This appalling case, where UK intelligence sharing has been linked to brutal torture, illustrates vividly why the National Security Bill needs to be improved.”
Responding on behalf of all three accused government departments, the Foreign Office said: “It would be inappropriate to comment on an ongoing legal case.”