A former West Belfast MP worked for MI6. according to claims heard by a BBC Radio Ulster documentary.
The programme explores the remarkable life of Bill Allen - a soldier, diplomat and writer who also ran a Belfast advertising company.
The Allen Identity chronicles how the former unionist politician rubbed shoulders with Sir Oswald Mosley, Adolf Hitler and Russian agent Kim Philby.
Born in 1901, Bill Allen was educated at Eton.
He worked for the family advertising business, David Allen and Sons, that was established by his Randalstown-born grandfather.
A keen traveller with a fascination for history, Allen became the Ulster Unionist MP for West Belfast in 1929.
Queen's University lecturer Paul Corthorn, who has studied Bill Allen's life, said Mosley and the Belfast MP were very similar.
"They moved, to some extent, in the same circles, they were both relatively young, at this point. They're both relatively wealthy as well. I think, like others, Allen was attracted to Mosley because Mosley was a dynamic, exciting figure."
Bill Allen eventually left the Ulster Unionists and defected to Oswald Mosley's movement known as the New Party.
He stood down after the 1931 election but continued his work for the family firm.
During the 1930s, he worked alongside Mosley and regularly visited Germany and Italy to try to raise money for commercial radio stations.
'Deal with Hitler'
Author Stephen Dorril, who writes about intelligence matters, said Allen and Mosley were very keen to strike an agreement with Hitler.
"They went to Germany and they wanted to get a deal with Hitler." he told The Allen Identity.
"Allen spent a considerable amount of time on this and did meet Hitler and all of the leading figures in the Nazi regime. It did get to the point where they were signing contracts.
"They had a number of companies to oversee this, and Allen came back and said he got the agreements of Hitler and they celebrated with Mosley with champagne."
Eventually Mosley and Allen fell out over money and political ideals, leading the two men to go their separate ways.
The former unionist MP was in military service during World War Two, as a member of the Household Cavalry.
Well-travelled with a good knowledge of languages, his skills were much in demand by military chiefs.
However, during the war he was questioned by senior officers about his past associations.
'An MI6 link'
Documents, obtained by the BBC from the National Archives in Kew, show that the former MP was interrogated about his relationship with Mosley.
Allen told his inquisitors that he was a loyal British subject, stressing: "I should state I have no interest other than to see an out-and-out victory which will restore and maintain the power and reputation of Britain."
After the war, he worked as a press attaché in the British Embassy in Ankara, Turkey.
He became friends with Kim Philby who was working for military intelligence and later, sensationally, defected to the Russians.
Writer Stephen Dorril believes Bill Allen had a role with military intelligence.
"All these kind of things suggest the MI6 link."
So did Bill Allen have a secret life?
His granddaughter Sally Lescher accepts there is some mystery about her grandfather.
"It's confidential, I would say. You know, if you're working for the government you don't talk to everybody about it."
After World War Two, Bill Allen settled down in County Waterford with his third wife, Natasha, who was from Russia.
In the 1950s, MI6 agent Kim Philby was a regular visitor to Whitechurch House, his home near Dungarvan, and he helped Allen write a book on the history of the family business.
The house is currently owned by Kevin Neville. To this day, he said, Bill Allen is regarded as an intriguing figure
"He was a character, was he a spy for England? I don't know but he had some interesting people around him," he said.
Allen continued to write other books and established a reputation as a historian. He died in Dublin in 1973 - a man of many parts. An adventurer, a successful businessman, a writer, a soldier - and, many believe, a spy.
The Allen Identity will be repeated on Wednesday, 25 March at 18:00 and will be available on BBC Sounds.