I remember telling my mum I was thinking of becoming a policeman. Fine, she said, because it's what I want that matters, not what anyone else wants for me. My mum's good like that. But then she added that if I did become a policeman she would never speak to me again. She wasn't messing about either; I honestly think she would rather I didn't have a job at all. Or was a criminal.

Anyway, I like talking to my mum, so I didn't become a policeman. And I'm not sorry. I think my interest had come mainly from cop shows on the telly. Watching Coppers (Channel 4), real police going about real police work, suddenly it doesn't look so appealing.

We're with Nottinghamshire police in Mansfield. The Criminal Investigations Department, or CID, which sounds exciting and means they get to wear suits. But in reality it means that when they come knocking at the door they're generally mistaken for Jehovah's Witnesses. Except there are four of them here at this house, to look into some stolen electrical equipment. Four! Maybe those cuts aren't such a bad idea.

It's usually Thomas Hodgkinson's door they're knocking on. The 24-year-old already has 19 convictions, and seems to be single-handedly keeping this lot in work. Not that they seem at all grateful. "I mean, I just know he's a shit, end of," says case investigator Michelle Tonkin. "And we just go and get him whenever we can. Providing we've got the evidence to do so, I hasten to add."

Tonkin is currently investigating the case of a stolen handbag. She visits the victim's house, has a look in the wheelie bins. Maybe the perpetrator is hiding in there. "Bearing in mind how immaculate the garden is, it seems odd that there appears a beer can right by the window," she says, spotting what might be crucial incriminating evidence. Actually, strictly speaking, that's a beer bottle, Michelle, but good spot. Nothing escapes her notice. She's like a hawk.

Sergeant Marcus Oldroyd meanwhile is searching another house. He's not impressed by the state of it. "How some people live is just beyond me," he says. "I'm not a snob by any means but the only way I can describe it is a shithole."

They like their faecal references. "It's true what they say about statistics," Oldroyd says later. "Burglars shit on their own doorstep." Meaning, they don't travel far to do their burgling, I think. And, o f an uncooperative witness, DC Louise Foster says: "As the famous saying goes – you can't polish a turd."

It doesn't get much easier even when they do catch someone and bring them in for questioning. By someone I mean Hodgkinson, because it's generally him. "No comment," he says, to every question. What size are your shoes, Thomas? No comment. I get the impression they'd like to beat the crap out of him. "I mean I'm a bit gutted that I wasn't around in the 80s, particularly before the Police and Criminal Evidence Act, because now we've got to abide by the law and stuff," laughs Louise Foster. Ha ha ha. "Sometimes I watch Life on Mars and think if only it was still like that," says another female colleague. Can you even beat the crap out of a shit? That's not going to leave very much (a fart?). Thomas Hodgkinson? No, we never had him in for questioning, can someone open the window ...

No, it wouldn't have been for me. Nice suits, but what's the point when you're working in a sea of raw sewage? Well, you think you are. And you think you know how to clean it up, but the law doesn't allow you to. And every piece of that sewage is saying "no comment" and laughing in your face. And you've got a chamois leather, but what's the point?

Ah, finally, here's something they might be able to deal with, a trespasser in someone's garden. But it might not be protected by the Police and Criminal Evidence Act, given that it's a snake. "I don't know what to do," says DC Neil Alsop. "I want to know if it eats detectives or not." He said that about a dog earlier on. It clearly doesn't (eat detectives), being a harmless scarlet king snake and not a deadly coral snake, but Alsop doesn't seem to know his herpetology. After a half-hearted attempt to coax the snake into a bucket, he gives up and calls in back-up. A woman in uniform turns up and calmly picks the snake up and puts it in a bag. I'm not sure if she's uniformed police or (more likely) RSPCA; but anyway, she's the most impressive person in this. By far.