The family of a former British soldier imprisoned in Turkey after fighting with Kurdish forces against Islamic State of Iraq and the Levant (Isil) in Syria has appealed to Theresa May to help secure his release.

Joe Robinson, a 24-year-old from Accrington, Lancashire, was arrested in Turkey last month and has now been charged with membership of a terrorist organisation, a crime that can carry up to 16 years in prison.

He served for one month in 2015 as a medic with the People’s Protection Units (YPG), a Kurdish group that is considered a terrorist organisation by Turkey but not by Britain. YPG forces are fighting alongside Western troops in Syria.

Mr Robinson’s family wrote a letter to the Prime Minister, calling on her to intervene despite any “geopolitical interests” Britain might have in not offending Turkey.

“We cannot let a young man, who did the right thing, go to prison. A man who made a change, who saved lives and defended our country's interests,” the letter reads.

“To do anything other than provide effective and immediate support to a man who is a British citizen, a veteran and a hero, is to show a deep disregard for your veteran forces, and to ally yourselves with an oppressive state.”