One of the so-called "Chennai Six" members says he feels "betrayed" by the UK government over his jailing in India.

Billy Irving, 37, said he could "never forgive" the Foreign and Commonwealth Office (FCO) for not doing enough to free him and his compatriots.

Mr Irving and five other British army veterans spent four years in prison on weapons charges, only to have their convictions overturned earlier this week.

The men, who always protested their innocence, were guards on a ship to combat piracy in the Indian ocean when they were jailed in October 2013 for carrying unlicensed firearms and ammunition.

Mr Irving, who returned to the UK on Wednesday, has now provided a scathing assessment of the British government's handling of the case.

Billy Irving (bottom left) and his five British compatriots. Credit: Chennai campaign.

Speaking to the Mail on Sunday, Mr Irving, from Renfrewshire, said he would struggle to forgive UK authorities.

"I can never forgive the UK Government and the Foreign and Commonwealth Office," he said.

'We would have been freed much sooner if they had really engaged in our plight and fought for us.

"I feel disgusted and betrayed."

Mr Irving's fiancee Yvonne MacHugh, who campaigned for his release, described former foreign secretary Philip Hammond as "next to useless and uninterested at best".

Mr Irving's family criticised Philip Hammond. Credit: PA

She accused current incumbent Boris Johnson of "hypocrisy" for saying the FCO had worked on the case "unstintingly".

"Billy and the other men would've been free two years ago if they had been truly there for us," she said.

Her partner described his ordeal - during which he contracted dysentery and lost three stone - as an "unbelievable nightmare" and spoke of his sorrow over being "robbed" of seeing his 33-month-old son William grow up.

Mr Irving said: "To finally smell fresh air and feel cold, wet rain on my face is the most fantastic feeling in the world.

"Now I just want to get to know my son, focus on being a proper father and spend time with my family."

The UK Government said the case had been raised more than 50 times at ministerial level and nine times with the Indian PM since October 2013.

A FCO spokeswoman said: "The UK Government was delighted that the men were released and the Foreign Secretary also paid tribute to those who campaigned for them.

"The Foreign Office worked tirelessly behind the scenes to reunite these men with their families."