The man on the park bench in Hammersmith, west London, was not happy. His responses to the police's stop and search were hostile, hinting at racial harassment – he was black – and worse. He demanded their warrant numbers. Nevertheless, he turned out his pockets and held his arms up, as parents in the children's playground opposite looked on.
Known to the police as a drug dealer, he was clean on this occasion. No drugs, and no weapons. One of his friends was less lucky: a check revealed an outstanding warrant for unpaid fines of £575 and he was carted off to the police station.
Last Friday afternoon, members of Hammersmith and Fulham's robbery squad were out patrolling. Searching for stolen phones; searching for drugs – but especially for knives.
The Home Secretary, the Mayor of London and the police argue that it is the most effective weapon: robberies and knife crime are inextricably linked. The police point to a 50 per cent drop in street robberies over the past couple of years and attribute it directly to stops and searches "disrupting" criminals.
"There are 13- and 14-year-olds for whom carrying a knife is becoming culturally acceptable," said Sergeant Stewart Ratcliffe. "The same people are doing street robberies. We find all kinds of knives – kitchen knives, machetes, we found one kid with a small axe. You'd be amazed what you can hide down the front of your trousers, over your thigh."
Sergeant Ratcliffe's counterparts around the country are under pressure to take more of these weapons, and the people who carry them, off the streets.
By last weekend, the number of teenagers knifed to death in London had risen to 11 this year, with the stabbing of the young actor Robert Knox, 18, in Sidcup, south London, in the early hours of last Saturday.
Of the 11 victims so far this year, nine were black or Asian. The last two stabbings, of Jimmy Mizen and Robert Knox, both white, appeared to propel the issue up the news agenda.
The resultant media barrage on knife crime saw the launch of a £3m government advertising campaign aimed at teenagers, but this was immediately derided by ethnic-minority youth workers. Several questioned whether resources had been targeted effectively and if the people making the decisions had a full understanding of what was happening on the streets.
The police are trying to analyse precisely this. According to the Met, there is a knife-related incident every 52 minutes in London and victims are more than twice as likely to suffer knife-inflicted as they are gun-related violence.
A survey of youth crime which was considered by the Metropolitan Police Authority – the body that oversees policing for the Mayor of London – last week found that the busiest period for youth crime is between 3pm and 5pm, when the schools spill out.
According to the British Crime Survey, widely held to be the most authoritative estimate of crime in the UK, "knife-enabled crime" (any crime where a knife has been seen) has remained stable at between 6 and 7 per cent over the past decade. Similarly, while the numbers of murders in the UK have been rising overall, the numbers involving sharp instruments – which includes bottles, glasses and screwdrivers – has remained stable.
An internal Scotland Yard report reveals, however, that the murder rate for victims aged 20 and under has trebled in the three years between 2005 and 2007. The biggest increase is in victims under 10, as tragically illustrated by the fatal stabbing of two children aged five and six in Carshalton on Friday night.
It is no surprise that many find the statistics confusing. A report by the Centre for Crime and Justice Studies at King's College noted this "area [knife crime] suffers from a lack of useful, specific, reliable, longitudinal research on the nature, extent, cause, motivation, frequency and possible growth of knife carrying. Without [this], designing and implementing programmes to reduce the incidence of knife carrying will be difficult."
Few surveys actually ask whether the knife carried is a penknife, which can be carried for lawful reasons, or something altogether more sinister like switchblades.
The Home Office-sponsored Offending, Crime and Justice Survey 2005 found that 4 per cent of 10- to 25-year-olds surveyed had carried a knife during the previous 12 months. Of those, four in 10 said it was a penknife and fewer than one in 10 said they had used it to threaten someone. Only 2 per cent said they had actually used it to injure someone.
But on the streets, at the sharp end, so to speak, the police of Hammersmith would beg to differ. On Friday, they were stopping and searching. Their area, like so many in London, is a mix of upmarket period properties in tree-lined streets, three-storey terraces, and pockets of 1960s housing estates and tower blocks.
It is to one of these estates that the police were called by a woman complaining that three youths were smoking cannabis outside one of the blocks.
As the car pulled up, one of the youths was spotted throwing a joint into the bushes. The threat of a sniffer dog and arrest if he didn't retrieve it, opposed to a caution if he did, saw the 20-year-old rooting through the bushes as his mother looked on.
The drugs were confiscated and after an initial flare of anger, the youths were let go.
A few minutes later, on the same estate, the police stopped a youth on a moped after he whizzed past the inside of their unmarked car. He was "a known thief", and had been warned about dangerous driving before. The moped was seized: it will cost him £200 to reclaim it.
"He's been arrested for assault in the past, and is linked to petty thefts and robberies," Sgt Ratcliffe explained. "He's also known to transport people on the back of his moped to and from robberies, so anything we can do to disrupt that activity we will do."
Driving around in their unmarked Mondeo, it was not long before they spotted a youth aged around 16, on a bike riding "without purpose" along Shepherds Bush Green.
He was arrested for robbery on the Green last month, and there he was, back at the scene, providing the police with the "reasonable grounds" they needed to search him. He recognised the police and succumbed to the search – a frisk, a look through pockets and the top of the shoes – without complaint. He said he was only going to visit a friend.
The search – including a quick weapon scan with a metal detector – revealed nothing. The necessary forms were filled in and he was sent on his way.
One of the tactics police used was to "stop for a chat" and see how a suspect reacted. Grabbing a pocket, running away or throwing something away, would give them additional grounds for a search.
And so it proved when the car pulled up next to two youths on bikes during a patrol of a low-rise 1930s estate.
One of boys, aged about 16, instinctively touched his top jacket pocket. A search turned up a small bag of cannabis, which the youth mumbled had cost him about £10. He was judiciously vague about where he brought it from. The police checked his mobile phone, which had a picture of a gun for a screensaver. But he had no real weapons secreted about his person.
His cannabis confiscated, he was given a caution. And so the patrol continued. A few other youths, known to the squad, were stopped. None was armed.
And there lies the nub of the problem. Home Office research has stressed how problematic it is trying to track down knives in this manner – the most recent report in 2003 noted that, out of almost 19,000 people stopped and searched, 7 per cent were found to be carrying offensive or dangerous weapons; of these, only 203 were arrested. The report noted that "hit rates are surprisingly low".
Despite the total yield for a four-hour patrol being just a couple of bags of cannabis, the police in Hammersmith were adamant that stop and search is an effective measure.
"It's about robbery, street crime and knife culture," Sgt Ratcliffe said. "It is all linked. The people who are carrying out robberies are also carrying the knives.
"Stop and search is an essential tool in taking them off the streets and hampering their ability to commit crime."
Additional reporting Sara Odeen-Isbister