Theresa May has said she will raise the case of two ex-servicemen from the North West jailed in India when she meets the country's prime minister Narendra Modi today.
Ray Tindall from Chester and Paul Towers from Bootle were jailed with four others after a court found they had entered Indian waters in 2013 without permission carrying unlicensed firearms. They insist they were conducting legitimate anti-piracy work protecting merchant ships.
Family and friends have conducted a high profile campaign to lobby for them to be freed.
Speaking to reporters as she flew to India, Mrs May said: "I will be raising the Chennai Six in my talks."
A Downing Street spokeswoman said: "This is a consular case that the UK government has raised many times with the Indians. I think ministers have raised it around 40 times, including with PM Modi five times. We will make the point that we want to see this case resolved as swiftly as possible, while recognising that India has an independent legal system."