Remember, it's your nightmare

It is dark and raining, and I am standing in an alleyway just off a suburban street in Selly Oak near Birmingham. The alley is an L- shape. The first bit is close to the street and has a security light, but then you turn and suddenly feel extremely vulnerable. This is a rat's tunnel, barely 3ft wide, with sides of sheet metal and wood that are at least 8ft high. It is a dead end. No one could escape, even in a movie.

It is scary here, even if you are not alone. I am here with about 10 people and I'm still shivering. And not just because it's raining. This is not a movie set, though there is a cameraman who says "darling" a great deal and a man in charge of "moonlight". But this is a crime scene first and a film set by happenstance. The resulting six minutes of television will not be a drama but a reconstruction. This is Crimewatch.

I feel as if that sentence should be followed by dramatic music, but music, dramatic or otherwise, is just one of the things never allowed on Crimewatch. It began in 1984 and next Tuesday it goes on air with its 150th programme. Over the years it has become an institution, featuring 1,742 cases and resulting in 603 arrests.The presenter, Nick Ross, has been there since the beginning and must get exhausted by people quoting back to him his catch-phrase about not having nightmares. Even fictional police characters, such as Prime Suspect's Jane Tennison, go on it to solve their toughest cases.

Some say Crimewatch is public service broadcasting at its best. Others find it the thin end of the real-crime-as-drama wedge. It is not the easiest of subjects to write about. It is tempting to poke fun at it. The reconstructions can seem wooden, with stylised non-violent violence and those careful questions directed at viewers. "Did you see that car/ jacket/ bracelet, etc?" they ask and you rack your brain, feeling as if you really must answer. The photofits can be fascinating, and not just because you recognise someone. "Look at that silly goatee," you say to the other person on the couch.

Eight million people watch Crimewatch, though, and it's not just for curiosity's sake. Perhaps we watch for the same reason we play the lottery. There is a slim chance - you never know - that we might recognise someone on screen. "I've never seen anyone I know but I keep on watching because I want to so very much!" says one addict. This is Neighbourhood Watch without the legwork, a way to do the right thing without putting ourselves in any personal danger.After every programme an average of 1,500 people ring in. They have helped solve the little and large, including cases such as Lin and Megan Russell's murders in Kent. Crimewatch can make you feel a good citizen just by tuning in.

Back in the alley, I am struck by the lack of cynicism. "I think it's because we know that we can really make a difference," says the director, Katie Thomson. I'm not sure, though. Certainly the atmosphere would be much blacker if it were all policemen or all journalists standing in this alley. I think it is because Crimewatch is done in the name of the victim. "I am always aware that the victim will be watching the programme," says the editor, Seeta Kumar. "You've got to keep their dignity. You've got to remember what they have been through. We are not just about catching criminals. We are about trying to recognise the victim and helping to resolve what has happened."

It does feel as though the victim is here in Selly Oak. She is a young woman who was raped one November night by a man who apologised for what was about to happen. He told her that she was the kind of girl he wanted to marry. Then he raped her. Afterwards he tidied up. He has been linked to six attacks, four in Birmingham and two in Nuneaton, and is known as the Midlands serial rapist.

Every Crimewatch programme features some 14 cases. Dozens are considered. Some are picked out by researchers from the papers or are put forward by police. For a case to be featured, there must be clues that can be put forward and there must not be a suspect. Cases are not chosen to balance each other out. Ms Kumar says she could not live with herself if she did that. She could not tell a victim that her case wasn't used because it would make the programme too grim. Sometimes they are included because it is feared that the suspect may strike again.

It is thought that the Midlands rapist may do so. Everyone on the set talks about the crime. Quietly. The sound technician says that, standing in the alley, it is impossible not to think about what she would have done. Crimewatch is meticulous on accuracy. A police officer is always on hand. They film only at the real crime scenes. If a crime happened at night, it is filmed at night. For the Midlands film, both filming days did not end until after 2am.

The actors speak only words that were said. This can sound ridiculous because real life simply is not like a Tarantino movie. "You're the sort of girl I'd like to marry," says Shaun Dellenty, who plays the suspect, to his alley victim. Crimewatch actors are often chosen for how they look, and Shaun was chosen for his sideburns. His most recent job was touring in "the Scottish play". The victims are all cast from Birmingham School of Speech and Drama students. "I wanted them to have that real sense of innocence," says Katie Thomson.

She has decided to show details of four of the attacks - though no real violence is allowed - and shorter versions of the other two. She has met all the victims. Four agreed to be filmed. She says that it is these interviews, shot in silhouette, that provide her reconstruction with its grit and its drama. The story line is organised around the appeal points. "I always ask, how do you make a film that will make people want to phone in? It has to move people and make them help," she says.

This is the trademark of Crimewatch reconstructions. Most real-life crime television shows are aimed at entertaining, and use all the techniques of drama to make life seem hyper-real. But Crimewatch takes real life and makes it less dramatic. It lets the victims keep hold of their own stories. "It is about real people and getting away from the soundbite," says Ms Kumar.

"Working on this programme is so humbling. You come across such raw grief and you see such courage." Back in the alley, it's a wrap. The crew heads for the next crime scene. I head for somewhere warm, and wish someone would just tear down this alleyway so it would not exist.