Tony Padman talks to the notably comic actor about taking on a straight role as propless Detective DS Khan in the cold case thriller Unforgotten.

It’s a sure sign that you have arrived when you get invited to introduce a major headline act like UB40 at the Live 8 concert in front of 250,000 people at Hyde Park. “Fantastic! What an honour to be asked,” remembers Sanjeev Bhaskar of that unforgettable moment back in 2005. But there was one slight hitch when he checked the clipboard showing the running order. “My name was there,” he says. “And in brackets it added, ‘Unless Ricky Gervais turns up.’”

Considering Bhaskar’s lengthy comedy background in shows like Goodness Gracious Me and The Kumars at No. 42, he was equally surprised to be cast as DS Sunil “Sunny” Khan in the new six-part drama series Unforgotten, which charts the police investigation into a ‘cold case’ murder that happened in 1976.

“It is a departure for me,“ confirms Bhaskar, 51, who co-stars with Spooks actress Nicola Walker as his boss, DCI Cassie Stuart. “When I was asked to audition I thought, ‘They’re never going to offer me the role.’ After reading the script, I knew I wanted to be a part of Unforgotten and I said to the writer, Chris Lang that I can’t wait to see it – not expecting that I’d get cast. It all begins with the writing and this is exceptional.”

We first meet Khan wearing a white protective police suit outside a demolished house in Willesden, where the remains of a young man have been discovered by workmen. It’s at the crime scene that both detectives make a startling discovery that will pave the way for their unstoppable, dogged determination to uncover the killer.

The cast of Unforgotten reads like the cream of British acting talent with Cherie Lunghi, Gemma Jones, Ruth Sheen, Brian Bovell, Trevor Eve, Bernard Hill and if that’s not enough, there’s also Sir Tom Courtenay. All have secrets that have remained hidden for years and as they are uncovered, their lives and those of others become shattered for ever. But can they ever be forgiven by those closest to them?

The fact that the murder goes back to the ‘70s resonates strongly with Bhaskar. He recalls: “I was 13 then and living with my sister and parents above a launderette in Southall. The National Front would try to sign up students outside my school and we regularly had ‘NF’ scrawled on our front door; I also remember the anti-racism demonstration that took place in Southall where the teacher Blair Peach was murdered.”

Bhaskar feels that Unforgotten is “very different to other crime dramas because of its historic element”. Another difference is that these are much older suspects than we normally see, who have lived long lives as Lang explores whether a person can live for decades with such a terrible secret without it showing.

“Showing what is happening in their lives and their loved ones is as important as uncovering the murderer. How this crime impacts on each other person is immeasurable. They are like aftershocks.”

Working with this cast has been as exciting for Bhaskar as getting the job itself. “I’ve said to myself, ‘How brilliant they were’,” he exclaims. “It’s an extraordinary cast and Nicola and I get to work alongside all these suspects. I’ve been touched by how big-hearted they are as actors and as people. These guys have nothing to prove and they’re as thrilled to be in this as me. I’ve found it humbling that they’ve let me be a part of their world and in their scenes.”

He adds that Walker said to him, ‘How lucky are we to work with them?’ “I told her that she’s one of them because she’s a brilliant actress, down to earth, friendly and generous.”

His summing up of his co-star is a mirror image of how I would describe Bhaskar himself, who is also unassuming and modest – in fact very similar to the gentle, good-natured TV presenter he plays in The Kumars at No. 42 who is over the moon to interview his movie heroes like Charles Dance, Daniel Radcliffe and Patrick Stewart. But then Bhaskar, who used to work in marketing, has always loved films and TV and counts Roger Moore, Billy Wilder and the series M*A*S*H as his favourites.

And while it’s true that comedy is what he is most associated with, he does have a full portfolio of dramatic roles to his name including Silent Witness, Lewis and a series of doctors in Indian Summers, The Indian Doctor and Jonathan Creek.

Sanjeev never got to introduce UB40 at Live 8 because Ricky Gervais did turn up. Still, 2005 was a great year for him because he was awarded the OBE and he married his actress-writer-broadcaster-playwright wife Meera Syal. They live in Highgate with their young son, and a daughter from Syal’s first marriage.

With a big smile on his face he says: “I’ve seen how Meera balances all these things together with being a parent and looking after our family members. It didn’t start off as a date or anything like that; we were friends for 10 years after meeting on Goodness Gracious Me and it evolved and grew into something. I think she’s amazing and I want to learn from her; she’s the talented one.”

Among the shows where he’s revealed his own talents outside of acting are as a stand-in presenter on Radio 5 Live’s film programme, Wittertainment, where he did a sterling job interviewing Eddie Redmayne, and more recently as the writer and presenter of the BBC documentary, Bollywood and Beyond: A Century of Indian Cinema.

And it’s a nicely understated performance that Bhaskar gives as DS Khan. He says: “What I find remarkable about him is that he doesn’t come with any baggage such as being a drinker or a gambler; McCloud had his horse, Columbo had his raincoat and I’ve haven’t got anything, so that’s remarkable – and good, because it allows the story to become the star and the viewer becomes the detective.”

Unforgotten starts on ITV1 from October 8 at 9pm