In October last year a group of fans of a TV show went on a day-trip. Emblazoned with “I Love 1973!” badges, they toured public baths where the morgue scenes were shot (“We were all so excited!” says “Yayster”, describing the trip on a web forum), visited the town hall (“We had a big debate on what side of the building Sam was on in episode one”), spotted police cars in the BBC lot that were used in the series, and ended with a themed quiz where the “Supreme Divs” pitted their wits against “The Geniuses”. True to their name, The Geniuses walked off with the grand prize of a signed DVD — and a pack of pink wafers.

The excitable “NorthCoastLad” summed up the mood: “If there’s a series three, we could tool around Manchester and kidnap the cast!”

Welcome to the weird world of Life on Mars fandom. And luckily for said cast (but putting a major spanner in NorthCoastLad’s plans, obviously) series two — which begins on BBC One on Tuesday — will be the last.

The cop show that made ludicrousness an art form included the excellent John Simm ( Sex Traffic, State of Play) trying not to laugh as he played the uptight cop Sam Tyler, who finds himself transported to 1973 — and made to work under the control of an unPC PC in the form of DCI Gene Hunt (Philip Glenister) — what GBH would look like if it had a hangover.

Is it all real? Is it all in his head? And why is everything beige? No one really knew — but the public loved it. And, being a “period” show, the nostalgia element meant some loved it a little too much.

Essentially The Sweeney meets Back to the Future, the premise also allowed the makers to combine the best two elements of any cop show: the procedural, evidence-based, clue-tracking methods of Tyler, and the approach favoured by Hunt — punching people really hard in the stomach.

Witness not giving evidence? Punch him in the stomach. Colleague disagreeing with you? Punch him in the stomach.

And, true to form, as I watch them shoot the second series on a slightly run-down Manchester back street in the baking summer sun of 2006, Glenister is here. He has just burst through a front door. He’s wearing a collar that looks set for take-off. And he’s threatening to punch someone. Really hard. In the stomach.

This scene kicked off — as is standard — with Glenister swinging the now-iconic Ford Cortina around as if he’s on an ice-rink.

“He insists on doing his own stunts!” says a rather pale Simm, who has to sit in the passenger seat. “Every time you see me in the car I’m clinging on to that handle. It became a good character trait — but it’s for real. I’m clinging on because I think I’m going to die.”

The residents of this slightly run-down row of houses look on. Some watchers are here specially. Michael Bugajski, 47, and Liz Rodgers, 41, have both travelled from miles away and are ecstatic that they have been allowed to park their vintage cars in the background of the scene.

“I just love the show,” says Bugajski. “And I love all the Seventies touches. I wanted my car to be part of that. I can’t wait to see it on TV.”

As we stand waiting for the next scene to be filmed, an old lady — a matchstick in a red dress — gets her hair sprayed as she readies herself to be used as a human shield by a kid wielding a wrench. Is she excited to be on screen? “I’m not looking forward to being punched up!” she says.

As we move to the alleyway where the wrench-wielding is to be done, the crew get to work, taking this cobbled back-alley back to the 1970s. Any double-yellow lines must be covered, masking tape put on UPVC windows and black bins replaced with battered metal ones. Fake pieces of wall are put over satellite dishes, even fake posters advertising glam-rock nights must be plastered over modern-day posters. Today the problem is alarm boxes. One resident isn’t in, and the crew have to scale the back fence to cover the box — though I’m assured they’ve been given permission to do this.

Not all problems are so straightforward. During a shoot in a particularly seedy part of town, they needed to move a car parked on a double-yellow line, but discovered it contained a man enjoying the services of a prostitute. Did they disturb him?

“No,” says the stand-by art director Daniel Taylor. “It wasn’t urgent. We waited until she’d finished.”

On the day I’m there, shooting is halted by a TV licensing man knocking on the door of a house while Glenister is filming a scene inside.

“He asked me if I was the owner,” says Glenister, who answered the door. “Does he think I normally dress like this?”

For willing residents, interior decorations were also put back 30 years. “We’re like a home improvement show, but in reverse,” says Luc Webster, the location manager. The team also claim to have created a new colour: greige. “It’s a mixture of grey and beige,” explains Taylor. “Perfect for the Seventies.”

Of course, this being the final series (though a spin-off series, Ashes to Ashes, set in 1981, is in the pipeline), the attention to accuracy may prove irrelevant. Fans will discover whether Tyler is really in the 1970s, or if he is in a coma and it has all been a delusion. The dedicated watchers who swarm the Railway Arms fan-site (domeofstars.com), pointing out minor inaccuracies and inconsistencies may find themselves stymied.

“The thing about Life on Mars,” says Simm, when I speak to him after the second series is in the can, “is that you can get away with anything. So the fans can talk about my LCD watch being the wrong colour, or say that model of radio wasn’t made until 1974, but if it’s all in my head, it just means I’ve imagined it wrong.”

So definitely no third series then? “No. I’ve had two years of wearing flares and those crazy boots — my feet are only just started to move properly again. I’ve Seventied out!”

Really? “Well,” he says, after a bit of thought. “I think I’m going to have to keep the jacket . . . Just so no one can sell it on eBay.”

Life on Mars, Tues, BBC One, 9pm

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