The prime minister, Tony Blair, will today announce new measures to help care for Britain's 77,000 runaway children.

He will propose that a personal adviser is assigned to each child when they are picked up by the police.

The initiative coincides with a Social Exclusion Unit report showing that one in four runaways sleeps rough and 5,000 commit a crime or are found begging every year.

The report reviews the work of the unit and says that the government's anti-poverty measures are starting to work but emphasises that many of the measures are "extremely long-term in character".