Henry Wuga was just 15 when he was interned early in the Second World War for writing a letter to his parents in Germany.

Almost 70 years later, Mr Wuga confirmed his long-held suspicion that it was only a declaration of his innocence by MI5 that got him released from prison.

Mr Wuga, now 85, with two married daughters and four grandsons, told his story as part of the BBC’s The Week We Went to War series, shown this week to commemorate the outbreak of the Second World War.

As a teenager he had been a Kindertransport child, rescued from Germany before the war started. His parents sent him to safety from his home in Nuremberg. Henry, then 15, arrived at Liverpool Street station on May 5, 1939. After just one night in a hostel, he travelled to Glasgow on the Flying Scot to the home of Jewish widow Etta Hurwich.

“I fell on my feet. She took me in and treated me like a son. I went to school. I was one of the lucky ones,” said Mr Wuga.

He spent an idyllic few months in Scotland, including four weeks at the home of artist David Sassoon in nearby Kirkcudbright. Mr Wuga stayed in Glasgow until February 1940, when he was evacuated to Perthshire — and that was when his troubles began.

“I sent letters to my parents through an uncle in Paris. My mother wrote back the same way. Because it was wartime, all the mail was censored. The authorities saw letters going back and forth in German and suspected they might have contained a code. So I was arrested and accused of corresponding with the enemy.

“I appeared at the High Court in Edinburgh in March in front of Sir John Strachan and convicted. I told them I was writing to my parents, but they didn’t want to know. I can’t blame the authorities for doing that because we were at war.”

He was sent to a remand home and a number of military barracks in northern England and Scotland, where he was billeted with captured German sailors “because I was under 17 and they didn’t know what to do with me”.

After two months, he was interned at Peverel camp in Peel on the Isle of Man. “Again, I was lucky because others were sent to Australia or Canada.”

He had already started speaking English while in Glasgow and used it whenever he could “especially when war broke out as it wasn’t a good idea to speak German”.

It was after the introduction of internment of “friendly aliens” that he encountered the man whom he suspected of being from MI5. “I was told I was his room-mate. When I asked him who he was, he said he had been a lieutenant in the Wehrmacht, and that he was a metallurgist who had been seconded to work for British Aluminium in Fort William. Both his English and his German were perfect.

“We tried to work out why a German officer was in a camp with Jewish refugees. The only explanation was that he was sent to spy on certain people, including me and others who had been involved with politics. He got me drunk one night and tried to pump me for information. One day he was taken to hospital — but we heard later that he had turned up in another camp.”

After eight months in the camp and at his third tribunal — and after his drunken night with the mystery German — he was finally cleared of corresponding with the enemy and allowed back to Glasgow.

He spent the rest of the war there and remained afterwards, eventually opening a renowned kosher catering business.

He carried the mystery of the German officer all those years. “Often, I asked myself, did they really suspect a 16-year-old boy of corresponding with the enemy?

“I asked my MP how to find out and he said to contact the National Archives. I did and they sent me a lot of information, including documents that showed MI5 said I was innocent. The British authorities were really on the ball — but they had to be,” he said.

Mr Wuga’s mother survived the war after being hidden by Catholic friends. She and Henry were reunited in Scotland after the war; his father had died earlier of natural causes.

Henry Wuga was awarded the MBE in 1999 for his work with the British Limbless Ex-Servicemen’s Association.