Rifleman Alec Jay went to war on May 22 1940. Five days later at the siege of Calais, any clues to his Jewish identity were hastily buried in the French sand as he was taken prisoner by the Germans, spending five years in captivity.

John Jay is now putting his late father’s story on paper. He has visited the places his father was held, tracked down a prisoner who knew him and found his name in PoW archives in Poland and Russia. What he cannot discover is what happened to the woman he left behind.

Netta Rose and Alec Jay’s first date was at a school dance in 1939. They were part of the same Jewish north London set and dated for some months before Mr Rose was sent to Calais.

During his incarceration, he never wrote home for fear of his religion being revealed. But the poetry he wrote made it clear he had not forgotten Netta. Believing her boyfriend dead, she married another man in 1941.

“I want to find her to learn a bit more about the woman my father was dating when he went to war,” Mr Jay said. “And if she wants to know about my father and to read the poems he wrote for her when he was a prisoner of war, I would love to share that with her.”

From a note written by his father, Mr Jay knows that Netta’s favourite theatre was the Golders Green Hippodrome and her favourite colour green. Asked what she would do if prime minister for a day, she had replied: “Resign”. She was said to resemble 1930s actress Jean Forbes Robertson.

Mr Jay does not know if Netta is a nickname, or how old she is. He can only assume that she was a similar age to his father, who would now be 93.

“The research for the book is almost done,” he said. “But I would like to fill in some of the missing pieces and for that I would dearly love to find Netta.”