THERE are all sorts of reasons why people go missing, many of them entirely innocent. There may have been problems at work, or a family row. Or someone may just have felt they needed to get away for a bit.

It is amazing how often people who have disappeared do just turn up again safe and sound, admits retired top policeman Allan Charlesworth.

“So we should never, ever give up hope,” he said.

Nevertheless, the longer a person has been missing, the greater the concerns for their safety.

Mr Charlesworth, who retired as deputy chief constable of West Yorkshire Police in 1999 and now lives in York, was involved in many missing persons cases in his career. Here, he talks us through a typical investigation.

• The report

The police get many reports of missing people. Very often, people turn up only a few hours after disappearing. So how do police distinguish between those cases, and the more serious cases where there is a real possibility somebody may have been abducted or even murdered?

The first report may be a tearful call to the police control room. A worried relative or friend might pop into a police station, or even stop an officer or PCSO patrolling on the street.

However that initial report comes in, all officers are trained to ask questions that will enable them to make a preliminary risk assessment, Mr Charlesworth said.

“The big questions are: Who? What? Where? When? Why and how?” he said. “Why has a person gone missing? Has there been a broken relationship? A family argument? Was the person depressed? Did they have health problems? Did they seem to be moody?”

Factors that cause immediate alarm bells to ring include if someone is considered to be vulnerable – a child, for example, someone who was depressed, or a young woman who was out alone late at night – and if there is any evidence of strange behaviour or broken routines.

That was clearly the case with Claudia Lawrence, Mr Charlesworth said. She had seemed perfectly cheerful the last time she spoke to her parents. But then she didn’t turn up for work, and didn’t meet a friend at the pub as agreed.

“That would have set alarm bells ringing.”

All missing persons reports are recorded and monitored. But cases such as that of Claudia are very quickly flagged up and passed on to a senior officer, Mr Charlesworth said.

• Initial investigation

The first steps will be to check the home of the missing person, for signs of a break-in, or any disturbance. “There will be checks made with the employer, to see if the person had any problems. Friends will be contacted, to see if she has been in contact or if they know where she has gone.” In a case which has been flagged up for immediate attention, all this will happen within a few hours of the original report coming in, Mr Charlesworth said.

• Incident room

If initial checks bring no results, CID detectives will be brought in. A police van or mobile police station will be deployed to the missing person's home, or along the route where they may have disappeared, to co-ordinate a local search. Uniformed and plainclothes officers will use this as a base from which to conduct house-to-house inquiries. At this stage, Mr Charlesworth said, officers will be considering the “clear possibility" that there has been a crime.

Back at the police station, an incident room will be set up. Here, interviews will be planned, briefings held, checks made with local hospitals and other agencies, and information gathered, sifted and prioritised.

• The media campaign

At about this time, the senior investigating officer might well decide that media publicity is needed. This can be a huge help in a missing person inquiry, Mr Charlesworth said.

It lets people know that a person is missing, and puts out in public details of what they looked like, where and when they were last seen or spoken to, what their movements might have been. A good campaign can also make ordinary members of the public care about the missing person enough to be on the alert, and to let police know if they think they may know something or have seen something that might help.

“It enables police to put across the human side – for example that this was a 35-year-old girl who went to a local school, always walked the same route to work. She could be anybody’s daughter. She could be your daughter. What the police want you to do is put yourself in the shoes of her father, so that you contact them with any information or sightings.”

Police need the public to come forward with any information at all, no matter how trivial it might seem, Mr Charlesworth said. “People may think that their information is irrelevant, but it may be the missing piece of the jigsaw.”

Media campaigns like this generate a huge volume of calls. These are fed back to police staff in the incident room, who sift through them, prioritise the information, review it constantly, and use it to draw up lines of inquiry. At this stage, the investigation is being handled as a major crime investigation.

• The search

A detailed search of the area around the missing person’s house, or of their route to work, may now be organised. This might involve local police officers, but also officers called in from other forces, as well as forensic specialists and even volunteers. There may also be wide-spread use of posters to supplement the ongoing media campaign.

• Motive and opportunity

The longer a person has been missing, the more concerned police grow for their welfare. The investigation will turn into a full-blown criminal investigation, focusing on the possibility of abduction or worse. Investigators will be thinking about motive and opportunity of possible suspects. If, following detailed forensics investigations of the home and the route to work, there are still no signs of a struggle or of violence, police will consider the possibility that the missing person may have been taken or harmed by somebody they knew.

“It is very unusual for someone to be abducted or murdered in this country by someone who has had no contact whatever with the victim” Mr Charlesworth said.