Sikh activists have accused authorities in India of torturing a British Sikh man who was arrested while on holiday in the country in early November.

Jagtar Singh Johal, from the Scottish town of Dumbarton, was detained by plain-clothes police officers in the Indian state of Punjab and is accused of involvement in the targeted killing of eight prominent Hindu figures, a claim rejected by his supporters.

Campaign groups say authorities subjected Johal to abuse, such as body separation techniques and electric shocks to extract a confession, as well as denying him access to British consular officials, his lawyer and family.

Punjab's chief minister, Amarinder Singh, has rejected the allegations of torture as "baseless" and police say they have "sufficient" evidence linking Johal to the killings, though no charges have been filed against him three weeks after his arrest on November 4.

Johal's MP, Scottish National Party politician Martin Docherty-Hughes, said consular access was only granted to the 30-year-old 10 days after his arrest.

"With allegations of torture, I and other MPs have reached out to the [Indian] authorities seeking their commitment to an open and transparent judicial process," he said.

We take all allegations or concerns of torture and mistreatment very seriously and will follow up with action as appropriate. British Foreign Office

"Jagtar's family and his local community in Dumbarton are gravely concerned for his welfare and we all hope that with openness and transparency, that this state of affairs will conclude with a satisfactory conclusion and that Jagtar can come home."

Both British Prime Minister Theresa May and the leader of the opposition Labour Party, Jeremy Corbyn, have voiced concerns regarding the allegations of torture, and Rory Stewart, a minister with Foreign Office responsibilities, has promised "extreme action" if the claims of abuse are proven true.

A spokesperson for the Foreign Office told Al Jazeera: "We take all allegations or concerns of torture and mistreatment very seriously and will follow up with action as appropriate. When considering how to act, we will avoid any action that might put the individual in question, or any other person that may be affected, at risk."

Sikh activism

A petition calling for Johal's release has picked up close to its 50,000-signature target, and Sikh activists have used the hashtag #FreeJaggiNow on Twitter to demand his freedom.

The Sikh Federation UK, citing Indian media reports, said there were suggestions Johal was being targeted for his own activism, specifically his role running a magazine detailing "atrocities during the 1984 Sikh Genocide" and using social media to "influence" Sikh youths.

Since the 1980s, images of Sikh men and their tortured bodies have come to be shuttled back and forth between India and then Sikhs across the world. The Johal case reawakens this. Ketan Alder, Lancaster University

In 1984, Indian Prime Minister Indira Gandhi was assassinated by her Sikh bodyguards, angry at the storming of the Golden Temple, Sikhism's holiest site, by Indian troops fighting Sikh separatists.

What followed was a campaign of mob killings and massacres targeting Sikhs by Gandhi's supporters, which left thousands dead and is referred to as a "genocide" by some activists, particularly among the vast Sikh diaspora community.

According to Lancaster University academic Ketan Alder, the Sikh diaspora has played a key role in drumming up awareness of Johal's arrest.

"There is a significant Punjabi-Sikh diaspora spread across the world, and this is particularly vocal in North America and Britain," said Alder, an expert on the relationship between religion and politics in South Asia.

"This is one of the reasons that Johal's case has been raised in the House of Commons (British Parliament) and by Sikh activists outside of India. It is this diaspora-homeland relationship which speaks to the heart of the issue."

Alder explained that Johal's purported activism documenting the abuses experienced by Sikhs during the 1980s made it difficult for Sikhs in the diaspora to separate his case from the wider narrative of Sikh suffering.

"Johal's media-led campaigns implicated the Indian state in human rights abuses and the killing of Sikhs during the ['80s]. Since the '80s, images of Sikh men and their tortured bodies have come to be shuttled back and forth between India and then Sikhs across the world. The Johal case reawakens this," Alder said.

"Sikh separatist campaigns in India were before, and again could be, partly driven by Sikhs abroad and their own senses of displacement."