Hundreds of Sikh protesters have chanted and made calls for the Indian authorities to set Jagtar Singh Johal free.
The campaign was set out to release Mr Johal, which took place on the streets of Birmingham with a protest at the Indian Consulate.
Mr Johal, aged 31 from Dumbarton was visiting India to get married and was seized by the Indian security forces on November 4th 2017.
Protesters claimed that he was arrested on trumped-up allegations and said he had been tortured daily.
The Indian security services have accused Mr Johal of plotting terrorist attacks in Punjab.
The protesters stood outside the Indian Consulate in Augusta Street in the Jewellery Quarter with banners and loud calls for his release.
Mr Johal’s MP Martin Doherty-Hughes tweeted: “Thanks to everyone campaigning in support of #FreeJaggiNow. My constituent & his family need full backing from the UK Govt to secure a fair judicial process.”
Earlier this year 78 MPs, including five from Birmingham, signed a letter calling on Prime Minister Theresa May to intervene.
Birmingham Edgbaston MP Preet Kaur Gill (Lab) wrote the letter, in her role as chair of the All-Party Parliamentary Group for British Sikhs highlighting the torture.
Among those backing it were Birmingham MPs Roger Godsiff (Lab Hall Green), Richard Burden (Lab Northfield), Shabana Mahmood (Lab Ladywood) and Khalid Mahmood (Lab Perry Barr).
Sikhs and Kashmiris living in Birmingham join protests against India’s Prime Minister
Mrs Gill told Mrs May: “In light of these shocking new allegations, I call on you to use all the diplomatic means at your disposal to ensure that the Government of India abides by the rule of law and ensures that Mr Johal is not subject to torture.”
She added: “I know that you will agree with me that it is intolerable that anyone, let alone a British citizen, is subjected to torture, and ask for your assurance that this matter is being dealt with at the very highest level and as a matter of urgency.”
The Indian security services claim that Johal was arrested for his alleged involvement in the murders of retired army officer Brigadier Jagdish Gagneja, RSS leader Ravinder Gosain and Pastor Sultan Masih, and for the funding of Khalistan Liberation Force.