The family of a Scots pirate hunter who faces a fourth Christmas in an Indian prison with other Britons are to deliver a petition to Theresa May calling for his release.

More than 400,000 people have backed the petition by campaigners trying to rescue Billy Irving, from Connel, near Oban, on the fourth anniversary of his incarceration.

He is among the 'Chennai Six,' who were seized by the Indian authorities on weapons charges, from an anti-pirate patrol vessel and are being held in the city's main prison.

Mr Irving’s young son William and fiancée Yvonne MacHugh will be at 10 Downing Street to present the petition.

In October 2013, Mr Irving was among 35 security men who were detained on board an anti-pirate patrol vessel.

The Scot, John Armstrong, Nick Dunn, Nick Simpson, Paul Towers and Ray Tindall are awaiting the result of an appeal to the Indian authorities.

Last week a Foreign Office minister visited them.

The petition, started by Yvonne, states it understood the British Government could not intervene in a foreign Government's processes.

However it added: "When innocent men are being prosecuted for a crime they have not committed, then they should have an obligation to protect the human rights and freedom of these men and have them released and brought home.

“These men devoted their lives protecting others."