LONDON - Tough new powers to tackle knife and gun crime on Britain's streets and growing alcohol-fuelled yob violence become law next week.

The country has been hit by a spate shootings and stabbings that police say are linked to gangs and a culture of violent "yobs" -- aggressive young people who drink or take drugs and attack those who challenge them.

"The new measures which come into force on Monday send the strong signal that weapons on our streets will not be tolerated," Home Secretary Jacqui Smith said of the powers.

"We are determined to prevent young people obtaining knives by raising the age from 16 to 18," she said of the laws enshrined in the 2006 Violent Crime Reduction Act.

The legislation cracks down on the manufacture and sale of imitation guns, doubles the maximum sentence for carrying an imitation firearm and criminalises the sale of a knife to a person aged under the age of 18.

Air rifles and guns also face much tougher regulation. Air guns are to be sold by firearms dealers who are registered by police with sales taking place face-to-face.

Imitation guns feature significantly in criminal acts ranging from nuisance cases and intimidation to armed robbery, the Home Office says.

In 2005 to 2006 there were 3,275 offences involving imitation arms, which accounted for about 15 per cent of all firearms offences in that period.

Knife crime among young people has also been rife.

Since 2000, youths aged 10 to 17 have accounted for one fifth of those who have been convicted of unlawfully carrying a knife.

Other powers that come into force include reviews of premises that sell alchohol if police believe they could be associated with serious crime or disorder.

Earlier this week Prime Minister Gordon Brown hammered out plans to extend the use of police stop-and-search powers and use undercover officers to tackle gun crime.

Brown also announced his intention to equip police with hand-held mini metal detectors in four hot-spot cities, London, Birmingham, Manchester and Liverpool, to tackle gun crime.