More than five out of six people convicted of possessing a knife in public are set free by the courts.

Of 380 people found guilty in West Midlands courts of having a blade in a public place, just 63 were given a custodial sentence.

The figures, which cover the 12-month period to the end of 2006 and are the latest available, were published in the same week that Home Secretary Jacqui Smith promised a major crackdown on violent crime.

Ms Smith, MP for Redditch, promised police across the country would be issued with 100 mobile search arches and 400 metal detectors to help catch people carrying knives.

She said police and prosecution services would be encouraged to press charges rather than giving a caution, particularly in "hot spots" where violent crime was worst - including London, Liverpool, Manchester and Birmingham.

And she pointed out the Government had doubled the maximum sentence for carrying a knife from two years to four.

But Conservatives last night claimed the measures were "empty rhetoric" because so few of those convicted were jailed.

The figures, published by the Ministry of Justice, showed that in England and Wales, 6,320 offenders were found guilty of carrying a knife in a public place but just 995 were given a custodial sentence.

In the area covered by West Mercia Police, 16 offenders out of 96 people convicted were jailed, while in Warwickshire just two of the 30 people convicted were jailed.

In Staffordshire, 19 people were jailed out of 91 people found guilty of carrying a blade in public.

David Davis, the shadow home secretary, said: "These figures betray Gordon Brown's tough rhetoric as yet more spin.

"This staggeringly complacent attitude to knife crime shows that Labour are part of the problem, not the solution.

"Only the Conservatives will put more police on our streets to catch and deter offenders and actually enforce the law so that violent criminals are sent to jail. We would also tackle the causes of violent crime, such as drugs and family breakdown."

A Home Office spokeswoman said: "The Government takes knife crime extremely seriously.

"Last year we increased the maximum sentence for carrying a knife from two to four years and whilst sentencing is a matter for the courts we expect anyone who might consider carrying a knife to be sent a clear message about the consequences.

"Sentencing guidelines also state that when a weapon is used to frighten or injure a victim, prison sentences should be increased even further. We are actively working with the police to deliver a tough approach to dealing with knife crime.

"This summer there will also be a brand new £1 million campaign aimed at warning youngsters of the dangers of carrying a knife. In addition there will be new police resources for hundreds of knife arches and search wands in local communities."

Sentences are decided by the courts, although the Government legislated to introduce a mandatory minimum sentence of five years' imprisonment for unlawful possession of a firearm, in 2003.

Gordon Brown announced a policy of "zero tolerance" on knives earlier this year. It followed a spate of high-profile attacks last year, including a string of fatal stabbings over the Christmas period.