Gordon Brown warned parents yesterday that they had a duty to keep their children under control - amid escalating public fear about youth knife crime.

Up to 20,000 families could face eviction from their homes if they fail to rein in their offspring, the Prime Minister said.

They are among 110,000 households in which children are thought to be at risk of becoming prolific offenders - and where authorities are to target special support.

Youngsters who carry knives were also threatened with being forced to spend Friday and Saturday nights carrying out hundreds of hours of community punishment.

After a series of high-profile stabbings, Mr Brown yesterday acknowledged that many people felt unsafe.

He said: "We need to make it absolutely clear to everyone that it is completely unacceptable to carry a knife."

While insisting that youngsters with knives were more likely than ever to be caught, prosecuted and "severely" punished, he repeatedly stressed that responsibility lay with their parents.

"I think all of us recognise that the first responsibility rests with the parent," he said.

A £100 million youth crime action plan is to be published today and Mr Brown said community punishments would be strengthened.

"We should tell offenders that they will be punished severely, including going to prison or a tough community payback."

He said police officers were stopping and searching more people than ever before and more cash was available for their work.

Of the 20,000 families where parents had "lost control", he said they would be required to sign contracts promising to improve their children's behaviour.

Those who failed to do so would be hit with tough sanctions, including eviction.

Mr Brown did not associate himself closely with Home Secretary Jacqui Smith, who was widely criticised for suggesting that knife offenders should be confronted with the consequences of their actions by visits to hospitals or meetings with families of victims.

Meanwhile, Tory leader David Cameron said: "If you are carrying a knife and are caught, you should expect to go to prison. Plain, simple, clear.

"Instead, the Government seems to have jumbled together a series of ideas that have not been thought through."