A son is trying to track down the final clues as to what led his non-Jewish father to volunteer and fight in the Haganah - and what he did during his service.

John Winton, a former police officer, said he was hoping to piece together his father Peter Samuel Winton's time in 1948 with the Haganah, which became the Israel Defence Force after the creation of the state of Israel.

Mr Winton, who now lives in Spain, said he had begun to look into his father's colourful past after his death 10 years ago. His father was 21 when he began volunteering in Israel.

"My father was an interesting man and a great supporter of Israel. But it was one area of his life which he did not really speak about. I would hear him when reports about Israel came on TV, saying things like 'Good old Moshe Dayan'. But when I asked him why, he would never say."

It later emerged that Mr Winton's father had signed a declaration never to reveal details of his time in the Haganah - on pain of death.

He had to swear to keep Haganah secrets

"It is very important for me to fill this gap in my father's life, he held a very deep regard and affection for Israel and at one time I believe he was offered a home there, with us," Mr Winton said.

"He always saw the good in people; he always went where he thought he was needed. I believe he joined up simply because he believed in the cause."

Mr Winton, who initially approached the Israeli Embassy in London for information, was given some medals from the state which were due to his late father, but he believes a full file on his father's record in the Haganah is held by the IDF.

He is only able to see the file if he prepares a legal document, in Hebrew, that proves his father is dead and that he is his only heir, before the IDF is willing to let him see the details of his father's time with the Jewish fighters.

Peter Winton, who died in 2002, wrote detailed letters about his time as a volunteer at post-war refugee camps in France, and later described how he crewed American Jewish-sponsored ships carrying displaced people from Marseilles to Haifa.

He wrote: "We carried 600 in each of four holds, 2400 men, women, kids. Conditions [were] barbaric, but, after what most of them had been through! Paradise! Because they were 'going home'."

He later wrote: "I went with some volunteers to Haganah. By then, six Arab countries tried to invade Israel, so 'Bighead' thought that Haganah needed me."

But Peter Winton said he had been ordered to sign a document after he left Israel, ordering him never to reveal what he learnt during his time with the Haganah.

It says he "swears not to reveal any secrets known to me under any circumstances, and in the event of my failure to fulfil this oath, I hold myself liable to a death sentence."