In an encrypted, password-protected file on Detective Chief Superintendent Steve Moore’s computer is a list of Liverpudlians that he likes to call his “focus group”.

To earn a place on Mr Moore’s list, an individual must meet one of three criteria: to have been shot at, to frequent a house, pub or office that has been shot at, or to have been warned by police of intelligence that his life is in danger.

Once on the list an individual will receive a noisy, early-morning visit from the Merseyside Police Matrix anti-gun crime unit and be served with a stark warning letter. It reads: “We know you are involved in gun crime. If you don’t stop we will make it our No 1 priority to put you in jail using every power we have; put you under surveillance; evict you from your home; get an ASBO against you; take your child away; stop and search you whenever we want until we find something.”

The people on the list are all male and aged between 16 and 29. Once one of these “impact players” is jailed another suspect is promoted to the list.

Mr Moore declines to say exactly how many people are in his sights. “Let’s just say it’s big enough to make a difference,” he says.

The technical term is “targeted disruption” but one policeman offers a better description: “We are in their faces all day long.”

This no-nonsense approach to gun crime is what Bernard Hogan-Howe, the Chief Constable of Merseyside, wants to see adopted across the criminal justice system.

When he stirred controversy by telling The Times this week that he wanted “very heavy” sentences for firearms offences, he was not so much condemning the judiciary as making a plea for a consistent, zero-tolerance approach throughout the system. But Merseyside’s zeal continues to be overshadowed by the failure, so far, to bring a murder case against the killer of Rhys Jones, 11, who was shot dead last August. Rhys was hit in the neck by a bullet fired in a long-running feud between the gangs of Croxteth and Norris Green that has terrorised the area for years. The killer fled on a bicycle.

A 14-year-old boy from Croxteth has been named on internet message boards as Rhys’s killer. The murder weapon has been found and the key suspect arrested and questioned but released without charge.

The new tactics for tackling gun crime — adapted from counterterrorism and organised crime strategies — are not always suited to dealing with “gangsters” who might still be at school. One Matrix officer involved in covert operations admits: “It’s difficult to gather intelligence on people who are little more than schoolkids, because there isn’t any — it’s not as if they have financial networks.

“Following a drug dealer on a flight to Málaga or tailing his Audi down the motorway is easy compared to following a kid on a mountain bike.”

The young criminals are also getting smart to police tactics. Rarely do they hide their guns in shoeboxes under their beds. Specialist police search teams are trained to look for weapons hidden in drains, parkland and derelict buildings and have found them in foxholes and badger setts.

More than 100 guns have been recovered on Merseyside since Rhys’s death, including Mac-10 and Steyr automatic weapons as well as converted replica handguns, stolen shotguns and military-issue weapons.

Mark Watts, who sold shooting kits comprising a handgun, a bag of ammunition and a silencer, was jailed last month for 15 years. His customers, police believe, were the young gangsters from Croxteth and Norris Green.

Watts was arrested last September after a three-day surveillance operation. Matrix officers raided a semi- detached house on a residential square in Haydock and found 11 handguns — hidden in drawers, cupboards and the bread bin — £15,000 in cash and a nylon shopping bag containing 35kg (77lb) of cannabis resin.

Watts has not told police who supplied him with the guns, nor who his customers were, but detectives have established that he had connections with criminal gangs in Manchester. A shell case found under the fridge in a house used by one of his associates was linked by forensic scientists to shootings in Manchester and Merseyside.

Among his haul of equipment were a number of German-made Reck blank-firing pistols converted to fire live bullets, and a random collection of museum pieces, including a 19th-century “pepperpot” gun — a revolver with four rotating barrels. The serial numbers on the modern weapons had been removed to prevent them from being traced.

Detectives are divided as to whether the discovery of 11 “clean” guns means that they are in plentiful supply or if the mish-mash of guns means that the likes of Watts are struggling to get their hands on high-quality weapons.

Such cases expose a crucial knowledge gap that hampers the fight against gun crime. Britain’s police forces have no reliable estimate of how many guns are in criminal hands.

There are operations against gangs smuggling weapons from the former Eastern bloc and to deter British Service personnel from bringing guns from Iraq and Afghanistan. The Serious Organised Crime Agency has recently been ordered to make tracing the supply of criminal guns one of its priorities. Next week the National Ballistic Intelligence Service will offer police the chance to trace the criminal history of every gun they recover.

Mr Moore says: “Even if you cut off the supply completely, the gangs can still arm themselves. In the States, gangs made zip guns which were crude but still lethal.”

The strategy he wants to put in place in Merseyside, and beyond, requires much more than zero-tolerance policing. It extends for a decade to involve schools, housing officers and social services in changing the lives of children at risk of being sucked into gang and gun culture.

In the light of problems with the Rhys Jones investigation, it requires a continual police presence to reassure vulnerable communities that they can speak out. “Ordinary people have got to believe that we are there with them for the long haul,” Mr Moore says.

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