When Anupam Kher received the script for a new BBC drama Mrs Wilson, he was initially a little miffed.

His character, Shahbaz Karim, did not even appear till “the last two pages”.

Weren’t they aware that “this would be my 514th film”, he said to himself.

But Anupam soon realised that he had been a little hasty in rushing to judgement. He was reading only the first section of a three-part drama. It was true his character did not appear until the very end of part one but then developed into a key role in the second and third episodes.

“When I started reading the (full) script, I was completely mesmerised,” he admits. “It’s great storytelling, amazing, complex. The point at which Shahbaz Karim comes in and puts a hook in for the next episode is amazing.”

Anupam has acted in quite a few British productions, almost appearing to corner the market in playing Indian dads — for example, Mr Bhamra in Bend It Like Beckham and Mr Bakshi in Bride and Prejudice, both directed by Gurinder Chadha, and as Sathnam Sanghera’s father in the BBC adaptation of the author’s autobiographical tale of a Sikh boy growing up in racist Wolverhampton, The Boy with the Topknot.

He may have done over 500 films, but it is unlikely he has done anything like this before. Shahbaz Karim is based in Lahore in the early 1930s where he works in a senior capacity for British intelligence as a controller in charge of English agents in the field. One of them is a man called Alexander (“Alec”) Wilson, whose funeral he attends in the UK in 1963, introducing himself to his wife by saying: “I wanted to pay my respects — (my name is) Shahbaz Karim. Alec was my best friend in India before the war.”

But Shahbaz, who says his eyesight is not what it was, makes one very bad mistake. He addresses the grieving widow, kneeling by her husband’s freshly dug grave, as “Dorothy”.

“Who is Dorothy?” she demands.

The woman Shahbaz addresses is, in fact, Alison Wilson, who was a secretary, Alison McKelvie, who had met and married Alec in 1940 when they were working in London for MI6, British counterintelligence.

Viewers in Britain have been gripped by Mrs Wilson and critics have raved about the drama, which the BBC has described as “inspired by real events”. The story moves backwards and forwards in time between the 1930s in pre-Partition India and the 1960s in the UK. When Alec dies of a heart attack at his home in London in 1963, Alison answers a knock on the door from a woman who announces she is “Gladys Wilson”, Alec’s wife, which indeed she turns out to be.

By and by, viewers learn there are four Mrs Wilsons.

The drama was shot mostly in Northern Ireland, with an Italianate mansion, Ballywalter Park, in County Down, “dressed up” cleverly with tropical plants and outdoor lanterns to resemble the governor’s residence in 1930’s Lahore.

In real life, Alexander Wilson was the principal and professor of English at Islamia College in Lahore. He also found time between 1928-40 to write 28 well reviewed novels, mostly spy thrillers, including The Crimson Dacoit. But when the journalist Tim Crook set out to investigate Alec’s life, it was as though the latter had been wiped out of history. The BBC drama is based both on his biography, The Secret Lives of a Secret Agent: The Mysterious Life and Times of Alexander Wilson, and the memoirs left behind by Alison Wilson.

“He saved a lot of lives,” is the response of a forgiving Shahbaz when Alison points out he has destroyed the lives of several women.

Anupam, too, is as philosophical as the character he portrays: “It does not remain (a story) about a man marrying four wives. It becomes (one) about human weaknesses, change of heart, change of so many things.”

Anupam appears to have made a successful transition from the Bollywood school of (over)acting to the more understated British style. He says he is glad he found the role challenging.

“I come from a Hindi medium school — I think in my native language,” he reveals. “Whenever I do an English language film or series, it makes my job more difficult —which I love. Only when you have a difficult job you can give your best.”

According to Ian Thomson, publicist for Snowed-In, the production company for the BBC drama, “Anupam Kher was picked because he is an absolute professional. We know his work.”