By Susannah Cullinane
The proliferation of knives across the UK has police worried, with Scotland Yard warning it is one of the most serious problems officers face. Can metal detectors beat the problem?
Most people at the trial noticed cameras, not the metal detector
He walks towards the silver poles, spots the police presence and makes a sharp U-turn. Officers, noticing his sudden change of heart, search him and find a knife.
The arrest that followed was one of the first made as trials of a metal detector at one of the UK's busiest bus stations begins.
With teachers calling for random weapons checks in schools and headlines warning of dangerous numbers of people - particularly the young - carrying knives, it is the latest initiative aimed at beating the problem.
The size of the task ahead was underlined on Thursday, when Metropolitan Police commissioner John Stevens said: "Gun crime has been reduced and people have moved over to knives.
"If people are carrying a knife for the wrong reasons then I think they should receive a mandatory sentence of two or even three years."
The metal detector trial is at Hammersmith in west London, which deals with tens of thousands of passengers each day.
It was chosen because it is used by people from all over London and is frequently attended by police called to deal with disorder incidents.
If the trial is judged a success, the equipment could potentially be deployed in the rest of England and Wales.
Commander Simon Foy, head of the Scotland Yard anti-knife crime initiative Operation Blunt, said the extent of the problem was difficult to define.
"We're more conscious of them if there's a stabbing or knifepoint robbery, but there's a grey area for burglaries through to assaults where a knife was used to intimidate.
"A considerable amount of violent crime is knife-related."
Fine or caution
Under current laws, possessing a firearm carries a mandatory five-year prison sentence, but offenders could be jailed for up to 10 years.
In contrast, anyone caught carrying a knife without good reason faces a maximum sentence of four years.
If the blade is less than three inches long the punishment could be as little as a £50 fine or a caution.
Police are concerned about the number of people now arming themselves with knives.
They say that young people aged 12 to 20 are more likely to be both offenders and victims in knife crime cases.
Last month Education Secretary Charles Clarke said schools could be given powers to search pupils for weapons, under plans to tackle bad behaviour.
After Luke Walmsley, 14, was murdered by a fellow pupil at a Lincolnshire school last year, Scotland Yard said hi-tech scanners would be offered to schools to help guard against knives.
An X-ray machine which can show weapons hidden under clothes is another of the tactics being used by police and officers have also been using hand-held metal detectors on suspects.
In Hammersmith, the installation of a metal detector seemed to appeal to many passengers.
Martha Brett, 55, from London, said they were a "fantastic" idea and that they should be at all stations, and possibly on public transport.
"Mostly for children - they seem to be carrying the knives, if it will protect one child I'm all for it."
She pointed out that a small, "but very sharp" Swiss Army knife on her keying had not set off the detector, but suggested it probably wasn't "prestigious" enough for children.
The metal detector is in fact set to a very high reading based on metal density, so it does not bleep at more innocent objects.
But police believe word has spread about the trial and fewer potential offenders were coming into the area where the detector was based.
"Some people being put off will be knife carrying," said Commander Foy, "there's the whole deterrent effect of this."
Commander Foy pointed to the deterrent effect of the trial
In terms of judging whether the trial was a success, Commander Foy points to the man who had been caught avoiding the detector.
He added: "The thing that will interest me most is what the officers say. Does this help officers do their job?"
Others are less convinced that the initiative will make a difference.
Another commuter was keen to keep the detector and officers battling crime in Hammersmith.
He said: "The police presence will put people off, but once they have gone away it will come back."