So much of this astonishing life was hidden from his son, who was moved by the story the Sunday Telegraph was able to share with him. Bishop Welby did not know, for example, that his father had Jewish ancestry, or an older sister called Peggy. He continues to wonder whether he has secret brothers or sisters.

He worked his way into the upper echelons of society on both sides of the Atlantic, using a series of adopted personas. But when he died of a heart attack in 1977, alone in a flat in Kensington, his only son – the person closest to him at the end of his life – did not even know his real name or birthdate.

Justin Welby, the future Archbishop of Canterbury, was only 21 years old at the time and studying law and history at Trinity College, Cambridge. He knew his father as an erratic and alcohol-dependent but “really, really brilliant” man who had lived an extraordinary life, although the true details were unclear.

“I lived with him, but I didn’t know him very well,” he said yesterday. Summoned down to London to complete the formalities after the death, the heartbroken son recorded the name of his father as Gavin Bramhal Welby, born on November 28 1914. Neither detail was correct.

The mistake was understandable, as Mr Welby Sr had hidden his identity many times. A chancer, draft dodger and adulterer, he had been sued for libel by a Cabinet minister. There was even a secret first wife that he never spoke of. But he had carefully constructed a respectable persona which allowed him to survive and to flourish, and without which his son would not have had a public school education or possibly a chance of high office.

Gavin Welby claimed a connection to the aristocratic Welbys of Lincolnshire and in particular Sir Charles Welby, the fifth baronet. He also suggested that his family owned a Scottish distillery. These untruths helped him befriend John F Kennedy in America, becoming so close that he even dated the future president’s sister Pat.

In this country, he won over senior members of the Conservative Party and the family of the deputy Prime Minister Rab Butler. He married Butler’s favourite niece, Jane Portal, who had been Winston Churchill’s personal secretary and who would become Justin’s mother.

His powerful connections helped him towards a career in politics and two failed attempts to win a seat in the House of Commons. Gavin Welby earned enough money to send his son to Eton – although he is said not to have passed on enough for Justin to pay his way on a daily basis, leaving him the poorest child in a school house that included two Rothschilds.

The present Bishop of Durham admitted last night that his father had told him “virtually nothing” about his true background, although the life that they did share together towards the end gave him a first hand insight into addiction and suffering.

“He drank quite heavily, and you know, he would say things sometimes when he had been drinking and you did not know what was true or not.”

The Sunday Telegraph was able to share remarkable new details with Bishop Welby about the life of a man who was actually born Bernard Gavin Weiler on November 28 1910 in Ruislip, on the outskirts of west London.

His father was “Hebrew” German emigre also called Bernard Weiler, who had moved to Britain from modern-day Germany some 20 years earlier. Mr Weiler Sr had an elder brother called Herrman who had refused call-up papers for the army and been stripped of German citizenship.

(Much later the synagogue in the village where they came from would be burnt to the ground by the SS, and Jews sent to Nazi death camps. Several people called Weiler from the area appear on the list of victims of the Holocaust.)

The senior Bernard Weiler became a successful ostrich feather merchant with premises in the Barbican and in Cape Town, South Africa. He lived in a large house with his English-born wife Edith, who was two decades younger, as well as a cook, a maid and a nurse for the children.

But the family fortunes were hit by the outbreak of the First World War in 1914, and the so-called “feather crash” which saw austerity and changing fashions kill off the demand for expensive feather-adorned garments and hats.

Anti-German sentiment was strong, so the family name was changed by deed poll to Welby and Gavin’s father took an agency job selling worthless “snake oil” drugs on sales trips to America. He sold an art collection, but in spite of failing health he was forced to continue making arduous week-long voyages across the Atlantic, cramped in steerage class.

Gavin took over this dubious business shortly before his father died. He was 19 years old. As he began to spent increasing amount of time in New York, the young man set about re-inventing himself. This part of the story did enter family history and Bishop Welby said recently that he believed his father had been a bootlegger during the Prohibition era.

‘I remember my father telling me [his mother] gave him £5 and put him on a boat. He said he went to New York in 1929 and traded whisky. When I was studying history, the penny dropped that Prohibition ended in 1933… so he was bootlegging. He was illegally trading whisky.”

After being told on Friday of the remarkable details of his father’s life, Bishop Welby said: “He would tell me how he ran alcohol with his ‘Italian friends’ as he liked to call them. But he kept so much to himself.”

The Sunday Telegraph has discovered that when Prohibition ended, the inventive young man – now calling himself Gavin Bramhall James Welby – was the New York import manager for the National Distillers Production Corporation.

His job was to supply Manhattan’s newly booming hotels and cocktail bars with the ingredients for their latest frozen, shaken and stirred alcoholic creations.

Aged 23, with a clipped English accent, and dark, debonair good looks, he modelled himself on the Hollywood star Cary Grant.

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