“I went to Camberwell Youth Court just after the stabbing and killing of headmaster Philip Lawrence with the then attorney general, Sir Nicholas Lyell MP.

“He was flabbergasted to see knives that had been taken from youths being handed back to them because the security guards couldn’t confiscate them. Later there was a Private Members Bill sponsored by Lady Olga Maitland MP, but it never got to grips with this problem.” 

A £3million “blood and guts” campaign launched by the Home Office last week to stem the teenage stabbing epidemic helped highlight the failing.

One image showed a bloody Swiss Army knife and screwdriver deeply embedded in a man’s torso.

The graphic scene is being used in a scheme warning teenagers about the harsh reality of knife crime via mobile phone messages and viral videos on the internet. But it served to underline the danger of the smaller folding blades youths are free to carry.

One long-serving police liaison officer, who did not wish to be named, said: “When the Home Office unveiled those pictures I was astounded to see they showed a Swiss Army knife when everyone on the force knows there is nothing that can be done to stop youths carrying them. 

Unless a suspect is caught with the blade fixed they are allowed to walk away with the knife from a youth court.

“I am aware of incidents where larger and more offensive weapons have been handed back to stop a backlash from a youth.”

Another PLO said: “Every day kids walk in with pocket blades but what can we do? They all carry them – and one thing’s for certain, these kids are not boy scouts.”

Last night Shadow Home Secretary David Davis slammed the Government’s worrying ignorance over the matter. He said: “It is bad enough that so many young people are carrying knives with impunity in the street, let alone when they appear in a court. 

“Only a zero-tolerance approach – including action to confiscate such weapons and punish those carrying them – will send a clear message that we are serious about tackling the problem.”

MITIE Security, contracted to secure all courts in Britain, has been told to lock away knives found during entrance searches, give the defendant a receipt and then hand the weapon back after the youth’s case has been heard.

Without any legal backing to confiscate the knife it is left to the guard’s discretion and regard for their own safety to report larger blades to the police. 

MITIE is understood to be calling an emergency meeting tomorrow to change its agreement with the Courts Service and stop any knife entering the building.

Dee Edwards of Mothers Against Murder and Aggression said: “All knives should be banned. These youths are not wood turners association boys.”

The Ministry of Justice was last night forced to mount an inquiry that is likely to lead to a change in the law recognising smaller blades as offensive weapons. A spokesman said: “Ministers are aware of the issue and have asked officials to look into the matter.

“Her Majesty’s Courts Service  take the issue of security within courts extremely seriously and have a rigorous system in place, including mandatory bag searches, bag scanners, metal detectors and surveillance cameras.”