Scot's plea to PM: 'Halt trade talks with India till my Billy is free'

They were detained after their ship strayed into Indian waters without permission in October, 2012.

India's Prime Minister is said to have assured Theresa May he is "closely" following the case Mr Irving and the Chennai Six.

During almost three hours of talks in New Delhi, May told Narendra Modi the plight of the so-called Chennai Six was "a case of concern" in the UK.

Now campaigners - including Mr Irving's partner Yvonne MacHugh - are calling on the Prime Minister to stop talks on trade deals with India until they are released and brought back home.

Ms McHugh said she and other campaigners had become exasperated that appeals promised that could finally see the six allowed home, were continually scuppered.

An appeal hearing was expected on Tuesday but families have been told that has put off till November 20. A planned appealing in October was also scuppered with families told it was because prosecutors had not shown up.

Ms McHugh said trade deals should go on hold until the men are released.

"The trade deals are such a huge bargaining tool.

"We would hope that the PM would use the trade deals as leverage and that the Indian government would see how important it is that we get them home and how ridiculous it is to keep them there. There is no reason to hold them.

"We just hope that the Prime Minister pursues the case a lot harder than David Cameron did.

"The Prime Minister is our only hope. She must use this opportunity to speak to them and ensure they understand the situation, that they are innocent and were actually protecting India and Indian fishermen. None of it makes sense. They were no threat to India whatsoever and they were actually protecting Indian waters from piracy."

The British men being held in India were all working for the US maritime security firm AdvanFort providing anti-piracy protection in the Indian Ocean when their ship was detained.

Once they boarded the vessel, Indian customs officials and police found 35 guns, including semi-automatic weapons, and almost 6,000 rounds of ammunition.

The prisoners were initially held at the notorious Puzhal Prison, near Chennai, for six months before the charges were inexplicably dropped.

But Mr Irving was prohibited from returning home until the conclusion of a police appeal which eventually led to the men being jailed.

Indian authorities claimed the crew had been unable to provide documents authorising their possession of the weapons.

The ship had 10 crew members of whom eight were Indians and two Ukrainians and 25 security guards — six British, 14 Estonian, four Indians and one Ukrainian.

Chris Matheson, the Labour MP for Chester has written to Mrs May to say the "the discussions on trade are a very good way to raise their cause”.

“I don’t think there should be any substantive talks on trade deals with India until they are released and brought back home," he says.

One lawyer said in January he believed that by March the judgement of the court would be reversed in an appeal.

Ms McHugh added: "There is an MP who asked about trade deals with India being on hold and we would hope all MPs ask for that.

"For three years all those men have suffered and their families have suffered and they should just release them now in time for Christmas before things get any worse.

"We got give a date for the appeal of the 8th of November but then we think it has been put off. We have been waiting since January for the appeal and the Foreign Office promised us that there would be no more delays and things would run smooothly but to date nothing has. It has been delay after delay .

"Every three weeks we get given a date, the public prosecutor doesn't turn up and then we are given another date three weeks later to the point now that dates don't matter. Until we hear something concrete I don't believe anything will ever happen."

British sources said Modi assured the May he was aware of UK concerns.

He reportedly pledged to consider whether or not there was anything that could be done by the two governments once the current appeal process has concluded.

Following Monday's talks, a UK government source said: "The Prime Minister raised the case of the Chennai Six and said that this was a case of concern in the UK.

"Prime Minister Modi said that they were aware of our concerns and that they were following the case closely, that there was a process that now needs to run - given that it has gone to appeal - and that once that process is complete, we should look at whether there was more that could be done between the two governments."

The campaigners previously published what they claim are legal arms licences issued to the jailed men by the British Government and have called on ministers to do "the right thing" by stepping up their efforts to free them.

The documents, supplied by the Department for Business Innovation and Skills, were delivered to the High Court in Madras.

It is claimed the licences authorised the export of arms and other equipment, which included semi-automatic assault rifles to the US maritime security firm AdvanFort, for whom Mr Irving was working.