Nearly 140 MPs and peers have written to Dominic Raab urging him to do more to secure the release of a young Sikh man facing the death penalty in India after a confession allegedly extracted under torture.

The letter calls on the foreign secretary to accept that Jagtar Singh Johal is being detained arbitrarily, and says at least three of the charges levelled against him carried the death penalty.

In the letter the parliamentarians wrote: “When a British national is arbitrarily detained, tortured, and faces a potential death sentence, all on the basis of trumped-up political charges, the British government must make clear this is unacceptable. This is a moment for the UK to take a stand and bring this young British man home.”

Signatories include the former Brexit secretary David Davis; the former international development secretary Hilary Benn; the father of the house, Sir Peter Bottomley; the SNP leader at Westminster, Ian Blackford; Sheffield’s mayor, Dan Jarvis; the former Foreign Office minister Lord Hain; the former Liberal Democrat leader Menzies Campbell; and Andrew Rosindell, a Conservative member of the foreign affairs select committee.

They claimed in their letter that Johal, who has been detained for three years, is a Sikh human rights activist from Dumbarton who travelled to India in October 2017 to get married and, three weeks after his wedding, was violently arrested by plainclothes police officers in Punjab before being “bound, hooded, and bundled into a car”. “We understand that his arrest was unlawful, amounting in effect to an abduction by the state,” they wrote.

They added, after his detention, “Jagtar was brutally tortured with electricity into ‘confessing’ his involvement in an alleged conspiracy to cause unrest through attacks on Hindu leaders.”

Jagtar is being supported by the legal NGO Reprieve, which said the charges – of procuring arms, conspiracy to commit murder and a terrorist act – all carry the death penalty in Indian law. It has been alleged he provided £3,000 to a Sikh planning to kill Hindus, charges he denies. Despite an extraordinary 145 court appearances, his trial has been repeatedly delayed at the request of the prosecution, and basic information to defence counsel denied.

Reprieve deputy director Dan Dolan said: “It’s baffling that the Foreign Office hasn’t sought Jaggi’s release. We’re talking about a young British man facing a death sentence, based on nothing but a supposed confession he recorded after being tortured with electricity. It is about as clear a case of arbitrary detention as you can imagine, but the government hasn’t acted to bring him home. Why?”

The issue is likely to be diplomatically sensitive for the prime minister, Boris Johnson, as he seeks to cement economic ties with India by travelling to see its prime minister, Narenda Modi, on a postponed trip, as well as to host Modi as a guest at the UK’s G7 gathering set for Cornwall in June. The wooing of India is part of a wider UK government tilt towards the Indo-Pacific that is likely to be a central feature of the UK’s ‘global Britain’ strategy.