Some shows have fans, some shows have obsessive fans and some shows basically have stalkers. As a rule, shows in the third category tend to be American. Over here, we’ve really only had Doctor Who and Monty Python — although it’s probably best to avoid dinner-party conversations with anyone who loves Blake’s 7. Which is why it’s a good job that the second series of the time-travel cop drama Life on Mars will also be the last.

Take these questions put by fans to the show’s writer, Matthew Graham, on a BBC website: “Are you drawing from Zen Buddhism, advaita vedanta, dzogchen, nondual philosophy? Is this detective seeking his true self? To wake up to who he really is? To ‘cheat death’ by realising he is the one who was never born and will never die?” asks Rowan. “The underlying stages of the life/death cycle could be present in this series, namely: numbness — shock at the situation; denial — this is not happening; anger — why me? Why here?; depression — decline; acceptance; development; renewal/rebirth,” adds Nicholas, before Simon moves into waters that would terrify a Trekkie: “Is there a reason Gene Hunt’s Cortina has a 1975 dashboard, GXL on one end and 2000E on the other?”

These fans, known as Lifers, have been hacking into the website of the series’s production company, Kudos, in a bid to discover the show’s ending, which has been dangled tantalisingly before them as “shocking” by a sadistic BBC. For nonLifers (we’ll avoid jokes about “getting a life”, as these people know how to write letters), Life on Mars is a fish-out-of-water dramedy about a 21st-century detective, Sam Tyler, played with understated elegance by John Simm, who receives a knock on the head and wakes up in 1973. Or in his own coma-stricken mind. Or, dear Rowan, quite possibly in adhipanna-sikkha, the Buddha’s third stage on the road to nirvana.

The gags revolve around Tyler’s struggle to fit into a CID unit plucked from The Sweeney, where coppers slap confessions out of suspects, jail people they think might one day commit a crime, and aren’t entirely sure how to spell “forensics”. By the end of the first series, it seemed certain that Tyler was in a coma, which should have been cured by an encounter with his father, but wasn’t. The show’s ratings beat the opposition senseless — in a soundproofed cell, one assumes — and it so charmed America that the uber-producer David E Kelley (LA Law, Chicago Hope, Ally McBeal) bought the format for ABC. For Simm, Life on Mars moved him from serious small-screen actor (The Lakes, Crime and Punishment, State of Play) to legitimate tabloid fodder. It comes as some surprise, therefore, to discover his delight at the show’s conclusion. “I don’t like overdoing things, and I get bored playing the same character,” he explains. “To be honest, I would have left it after [series] one. But this was such a big hit, and people love it, so you’ve got to give them another. I think the concept would go stale in a third series. There’s only so many times I can roll my eyes and look disgruntled. When I went to see the producers, they said, ‘We want your audience, and you should be having ours.’ I thought, ‘Yes, get 7m instead of being on BBC2 in an amazing programme and getting only 4m. Why not? And if you can make this script — which is ridiculous — even slightly believable, then you truly are an actor, my son.’ I’m very proud of it.”

Certainly, in series two, the script becomes even more surreal, with Tyler’s hospital-bed nightmares pushing ever further into 1970s Manchester. The silliest moment by far is a trippy version of the children’s series Camberwick Green, in which Tyler and his boss, Gene Hunt, appear as Plasticine characters. Even so, it was the physical and emotional strain that really tested the fame-shy Lancashire lad.

“I’ve lived away from home for two years, and I’ve missed my little boy growing up.” He looks down at his hands pensively. “Life creeps in, claps you over the head and says, ‘What about me?’ I’ll never get those years back. He was blaming me in the end. I’d say, ‘Can I read you a story?’ He’d say, ‘Why don’t you read me a story when you come back?’ That would be the last time I saw him for a week. I was sitting on the train, thinking, ‘Nothing’s worth this.’”

This travelling issue could explain Simm’s complex relationship with Hollywood. His next project is to play Van Gogh in The Yellow House, a Channel 4 drama. He was up for a mainstream film with a Hollywood star, but opted for this instead. “It was unturndownable, really good writing,” he shrugs. “How do you say no to Van Gogh so you can play somebody’s mate in a Hollywood blockbuster?”

Yet he clearly resents Brad Pitt taking his role as the journalist Cal McCaffrey in the movie version of the newspaper-set thriller State of Play. “I mean, he’s Brad Pitt — I’m sure he’s going to be perfectly believable as an undercover reporter,” he sniffs. “It is a bit annoying. Just as long as he knows he’s playing me.” So, what does he want from Tinseltown? He sighs. “When I became an actor, I wanted to be a film star, of course.” He sounds faintly exasperated. “I went out there to do a pilot, but I would have had to sign for five years, and I was thinking, ‘I could do better TV shows than this in England and not sign my life away.’ If they want me to do a film, they know where I am. If they don’t, I’m not bothered. There’s such a lot of bull, which I find unbearable after a while. I’m not desperate for it.” So, after The Yellow House is a children’s TV show: “My son will love it — it’s for him.”

The comparisons with Tyler are obvious. Where Sam tries to flee 1973 — despite a doting WPC girlfriend, the power to do as he pleases with impunity and enough foresight to win big on the Grand National — Simm rejects primetime ratings for the sake of his craft. He’s also rejecting obsessive fans, cult conventions and the chance to spend his life as our very own William Shatner. So perhaps it’s not so crazy after all.

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