Prime Minister Gordon Brown said on Monday people carrying knives would be "caught, prosecuted and punished" as he defended the government's handling of knife crime following a spate of stabbing deaths.

But his message was overshadowed over claims from opposition parties that the government had already backtracked from a "half-baked" policy to force those caught with knives to visit hospitals to see stabbing victims for themselves.

"We need to make it absolutely clear to everyone, but especially young people, that in our country there are boundaries of acceptable behaviour, that it is completely unacceptable to carry a knife," Brown told his monthly news conference.

Four fatal stabbings in one day in London last week, taking the total killed with knives in the capital this year above 50, has returned the issue of violent crime to the top of the political agenda.

The capital's Metropolitan Police Service says tackling knife crime has now overtaken counter-terrorism as its main priority.

Senior Scotland Yard officer Alf Hitchcock, the government's newly appointed "knife tsar", said stab injuries had become more severe and were being committed by younger offenders.

Brown said the government was taking a range of measures to reduce the menace of knife attack, including more visible policing, greater stop-and-search powers, increasing use of metal detectors and tougher prison sentences or community punishments.

"It is a combination of prevention, enforcement and punishment," he said. "I wouldn't want people to think it is one measure alone."

Early intervention would be extended to 20,000 families where children were falling out of control, with the threat of eviction held over those who failed to cooperate.

Although overall crime was down by a third, Brown acknowledged there remain persistent problems with knives, guns and gangs.

"I accept that as long as young people, or any person, feels unsafe in our streets and our neighbourhoods, the job is not done and a huge amount is still to be done," he said.

"Let us be clear, if you carry a knife . you will be caught, you will be prosecuted, you will be punished."

However, shortly after Brown's announcement, Home Secretary Jacqui Smith found herself accused of abandoning a policy outlined on Sunday which indicated those convicted of carrying knives should visit hospital emergency wards in an attempt to confront them with the reality of stab wounds.

The plans have been criticised by criminal justice experts and the families of victims, who say they would have little effect.

"We are not, and I have never said we are, proposing to bring young people into wards to see patients," Smith told MPs, saying the plan was to bring young people "face to face" with the graphic consequences of knife crime.

But Conservative Shadow Home Secretary Dominic Grieve said the government had performed a U-turn.

"It's going to give the impression that the government is in fact constructing policy in three days, abandoning it in three hours, and that this is gimmickry," he told parliament.