In a personal warning to the Home Secretary, Charles Clarke, Ellie Roy, the chief executive of the Youth Justice Board, says that overcrowding has led to large numbers of juveniles ending up in prison-run institutions, which she warns are not appropriate for vulnerable children, and that some 18-year-olds may even have to be sent to adult jails if the situation continues.
In the document sent last week to ministers and prison chiefs, Ms Roy expresses concern that the rise is partly down to the accelerated use of anti-social behaviour orders that have been trumpeted by ministers as a successful measure in tackling persistent offending by young delinquents and keeping them out of jail.
This came in the same week that Tony Blair launched a crackdown on anti-social behaviour, including court powers to impose curfews on at-risk teenagers who have yet to commit an offence and a taskforce set up to improve respect for others in society.
However, prison reform groups have attacked the Government for resorting to quick-fix measures and for not tackling the causes of youth offending.The Howard League for Penal Reform said the Government had to take responsibility for any deaths of children in jails.
"The result of locking up increasing numbers of children is that it exacerbates anti-social behaviour because 90 per cent will come out and commit a crime," said Frances Crook, its director.
"The first thing he [Mr Blair] does after his holiday is to target children."