Actor, comedian and impressionist Alistair McGowan was born in Evesham, Worcestershire on 24 November 1964. He is best known for his BBC comedy show The Big Impression. In 2007 he appeared on Who Do You Think You Are?, where he was surprised to discover that his father was from India.

In 2003, McGowan’s father, George, died. Collecting documentation to register the death, Alistair noticed a small detail on his father’s birth certificate. His father, he discovered, was an “Anglo-Indian”. But what exactly does this mean? Why did George, who emigrated from the subcontinent to England in 1953, never mention any Indian ancestry? As Alistair talks of his closeness to his teacher father, “my best friend”, it’s clear there’s a real need on the comedian’s part to discover more.

Accompanied by his boisterous uncle, Rusty, Alistair’s journey into the past begins in the noise, heat and bustle of Calcutta. It’s a trip he approaches with some trepidation. “I’ve never been a big traveller really,” he says. "I’m quite good at France or Italy, at weekends, but I’ve never been a backpacker.”

His grandfather Cecil, Alistair discovers, was a fitness fanatic who had a well-equipped home gymnasium at his home near the port of Calcutta. Cecil worked as a foreman at the docks. This kind of responsible yet non-managerial job was common for Anglo-Indians, who were mistrusted by the ruling British elite.

This suspicion, Alistair learns, was in sharp contrast to earlier years. The British first became established in India in the early 17th century, gradually achieving economic and political control through the East India Company. Wanting children in the region to grow up with the values of the British, the company actively encouraged its male employees to marry Indian women. This, it seems, is what must have happened with one of Alistair’s relatives.

The reality of this lineage comes home to Alistair when he sees a picture of his great grandparents, Richard and Isabelle. “They look completely Indian,” he says. He also learns that his great grandfather was from the city of Allahabad, which lies on the shores of the Ganges and its tributary, the Yamuna river, in the north Indian state of Uttar Pradesh.

In Allahabad, Alistair sees telegraph operator Richard’s grave in an overgrown Christian graveyard, a somewhat perilous undertaking because of poisonous snakes that have made their home amidst the dead. However, this isn’t just a case of meet the ancestors: in addition, Alistair encounters a whole branch of the family that he didn’t know existed, stolid and middle class folk who live in the centre of Allahabad.

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Yet Alistair is still searching for evidence of his own Indian heritage. For this, he needs to go back another two generations. Richard’s grandfather, who bore the unlikely name of Suetonius, “married a Mohammedan woman of nobility”. A follower of the Swedish philosopher and mystic Emanuel Swedenborg, who rejected the idea of the Trinity and emphasised instead a mix of good works and faith in Christ as a way to salvation, Suetonius was as a deputy magistrate. But perhaps most astonishingly, he was Suetonius Jr.

As for John, father of the short-lived Suetonius Sr, he’s arguably the most noteworthy of Alistair’s forebears. Back in London at the British Library, Alistair meets military historian Tony Heathcote. When John McGowan first went to India, he was an ordinary soldier. On 12 January 1765, he married Maria de Cruz at Fort St George, Madras, a name that possibly explains family stories of Portuguese lineage. John McGowan was evidently a gifted soldier, who rose through the ranks to become a Major General, a wealthy man who left an estate that included three elephants.

He was also from Ireland, not Scotland as Alistair had imagined. The comedian looks genuinely shocked. “My name is Seamus Singh…”