Jagtar Singh Johal, 38, from Oxhill in Dumbarton, was arrested in November 2017, weeks after his wedding in the Punjab region, and remains in custody despite not being convicted.
His brother, Councillor Gurpreet Singh Johal, met the Labour Foreign Secretary Yvette Cooper in London on Monday to discuss the case but was dismayed by the outcome.
Afterwards, he urged the UK government to provide “diplomatic representation” to bring his activist brother home.
Jagtar Singh Johal was cleared in March by an Indian court of one of the cases against him, raising hopes that some progress might be forthcoming.
Foreign Secretary Yvette Cooper and Labour Councillor Gurpreet Singh Johal.
Speaking after the meeting with Cooper on Monday, Gurpreet Singh Johal said: “They failed when they had an opportunity after the acquittal in March – with the trade deal.
“They now have another six to eight-week window of opportunity and, if Yvette Cooper does not change her stance, then my brother could be in jail for a very long time.”
In the eight years since Mr Johal was detained, eight foreign secretaries have been in post and the family have been assured repeatedly the case is being raised with Indian officials.
But the latest meeting with Yvette Cooper, who became foreign secretary in September, left his supporters frustrated by what they felt was a lack of “engagement”.
Gurpreet Singh Johal told BBC Scotland News: “It was one of the most disappointing meetings I’ve had with a foreign secretary.
“When we thought we making progress with the previous foreign secretary and they were taking steps to bring Jagtar back home, today it’s felt backwards.”
When he was arrested, Mr Johal was accused of being a member of the Khalistan Liberation Force, which has carried out attacks in the Punjab region.
He was later charged with conspiracy to commit murder.
His supporters say he was tortured into signing false confessions – a claim denied by the Indian authorities.
They believe he was targeted for blogging about alleged human rights abuses against the Sikh community in India.
They believe an opportunity to secure his release was missed after the acquittal in March because the remaining cases are based on substantially the same evidence.
‘Time to bring him home’
Dan Dolan, deputy chief executive of the human rights charity Reprieve, said the family have been promised once again the case would be raised but that stronger action was needed.
“We really need this government to say it’s time to bring him home and take the necessary diplomatic steps to make that happen,” he said.
He added: “Unless the UK government takes stronger action, Jagtar will at best spend decades in prison, in a never-ending trial with no evidence, and at worst be sentenced to death and executed.”
A spokesperson for the Foreign, Commonwealth and Development Office said: “We continue to raise concerns about Mr Johal’s prolonged detention at every appropriate opportunity with the Government of India, and we have made clear that faster progress is needed to reach a resolution, including a full investigation into Mr Johal’s allegations of torture.”
Gurpreet Singh Johal pictured with Scottish Labour leader Anas Sarwar and Cllr David McBride campaigning for the Labour Party