It will be harder to get youths off the streets in a recession, the Tories say
The number of young people in England not earning or learning is increasing, figures suggest.
People aged 16 to 24 not in work, education or training went up by 94,000 to 850,000 between 2003 and 2007.
The Tories, who obtained the figures, said it was "tragic" the government had done "so little to help" young people during these "boom years".
The government blamed population growth and said the figures included disabled youths, carers and those on gap years.
Shadow skills secretary David Willetts obtained the figures, which were taken from the annual population survey, in a written Parliamentary answer.
He said the number of unemployed youngsters not in education, employment or training - so-called "Neets" - had risen in 47% of local education authority areas in England while it had fallen in only 25% of them.
Mr Willetts said: "Even in the years when, as we now know, Britain was in an unsustainable boom, the number of Neets was rising.
"It is tragic that ministers have done so little to help Neets during the fat years. Now that we are entering the lean years, it will be harder than ever to tackle this urgent social problem."
The greatest concentration - 24,000 - was in Kent and the lowest figures - 1,000 - were in Poole, Barnet, Swindon and North Somerset.
The biggest increase was in Hillingdon, where the numbers had trebled to 6,000, while the biggest reduction was in Barnet, falling by 80% to 1,000.
For the government, Skills Minister David Lammy said the Conservatives were being "disingenuous" because the figures included youngsters who care for parents or children, people on gap years, the independently wealthy who own their own properties, disabled people and those with mental health problems.
"Strip those young people out and actually the numbers are going in the right direction," he told the BBC.
He said the government was raising the age at which people have to be in school or training to 18, introducing vocational diplomas alongside A-levels and had "rescued" apprenticeships, which had been on the decline.
He said everyone needed qualifications - even youngsters who had been excluded from school - and said the government was funding "entry to employment courses".
A spokesman for the Department for Innovation, Universities and Skills said population increases also played a part and there were more young people in the population who were aged 16 to 24.
The number classified as "Neets" had remained more or less static as a proportion of the total - and almost a third of those were looking after their family or home, a spokesman said.
"The most recent statistics from 2007 show that the proportion of those aged 16 to 18 participating in education or training was at its highest ever rate at more 78%.
"But we must do more which is why we have taken the historic step of raising the participation rate to 17 by 2013 and 18 by 2015."
There were more apprenticeships and learners' choices were being widened with the introduction of the Diploma.
A study by the National Foundation for Educational Research just published by the sister Department for Children, Schools and Families, focusing on those aged 16 and 17, found "Neets" fell into different groups.
More than two fifths were generally positive about learning and very likely to participate in education or training in the short-term.
A similar proportion faced a lot of personal and structural barriers, and were likely to remain Neet in the medium-term.
A fifth were classified as "undecided Neet" - they did not face significant personal barriers to participating in education or training but were dissatisfied with the available opportunities.