London, Aug 7 (IANS): The British government has “abandoned and betrayed” six former soldiers jailed in India for carrying firearms while protecting boats from pirates, the sister of one of the incarcerated men has said.

The men -- Nick Dunn, Ray Tindall, Billy Irving, Paul Towers, John Armstrong and Nicholas Simpson -- who were arrested in 2013, were among 35 crew members sentenced in January by an Indian court to five years in prison for carrying unlicensed firearms, the Guardian reported on Sunday.

They were held while working for an anti-piracy security company protecting commercial ships off the coast of Africa in the Indian Ocean.

The men, who have been backed by more than 20 MPs, including former Prime Minister David Cameron, have consistently maintained their innocence and launched an appeal to overturn their sentences.

Now Nick Dunn's sister has urged Prime Minister Theresa May and Foreign Secretary Boris Johnson to intervene in the case amid concerns that the men's mental state was beginning to deteriorate.

“Nick's always maintained that he feels abandoned and betrayed by the government and the country that he once served,” Lisa Dunn told the Guardian.

“Now that we have a new government in place, I would like to personally reach out to Theresa May, Boris Johnson and Alan Duncan (Minister of State for Foreign and Commonwealth Affairs) and respectfully request that they continue to keep this case at the top of their agendas as we have been assured many times previously."

Lisa said the British government had issued the licences for the weapons, including semi-automatic G3 assault rifles, which the Indian courts have claimed are automatic weapons and, therefore, prohibited, the Guardian said.

Last month, Edward Bell, the British government's head of export controls, confirmed to the Indian court that Vince Cable, the then business secretary, granted licences for the firearms in 2012 and 2013.

Cameron made a personal appeal last year to Indian Prime Minister Narendra Modi on behalf of the Britons, who had served in Afghanistan and Iraq. Newly-appointed Minister for Asia, Alok Sharma, also raised the case with India's External Affairs Ministry in July.

“I appreciate and understand that the government have spoken to various Indian counterparts over the last nearly three years, but for the evidence that's there it's beyond belief that our government haven't pushed harder," the Guardian quoted Lisa as saying.

The men's prison conditions are said to be dire. Lisa said the men sleep on concrete in cells infested with snakes and rats, using a hole in the ground for a toilet.

Last week the men's families went to Downing Street to deliver a petition signed by 375,000 people demanding that the government secure their release.