Record numbers of young people are not in education, work or training, government figures revealed today, prompting fears that a generation will be lost to the recession.

One in six adults aged 18 to 24 in England are so-called "neets" (not in education, employment or training), the Department for Children, Schools and Families statistics from April to June show.

This amounts to 835,000 – 100,000 more than this time last year. The proportion of neets rose to 17.6% of 18- to 24-year-olds, from 15.5% for the same period last year.

The rise is thought to be fuelled by the recession and a shortage of jobs for young people. The Liberal Democrats said the surge showed young people were bearing the brunt of the economic downturn.

The government had promised to cut the number of neets aged 16 to 18 by two percentage points by 2010, from a baseline of 9.6% in 2004.

David Laws, the Liberal Democrat schools spokesman, said: "Labour claimed it would reduce the number of neets. Instead it has failed spectacularly and there are now more than ever.

"The government has not given young people the support they need and risks creating a lost generation."

But the chancellor, Alistair Darling, standing in for the prime minister while he is on holiday, said the government was doing all it could.

"At the end of last year we had record numbers of young people in education and training," he said. "We will, this September, be able to guarantee 16- and 17-year-olds education or training.

"And from the beginning of next year we will be able to guarantee people who have been out of work for a year either a job, training or further education.

"All of that is important, so we don't repeat the mistakes that were made 20 years ago, where a whole generation of people were lost. We are determined that will not happen again."

Iain Wright, minister for 14- to 19-year-olds, said: "It's important to remember that these figures are seasonal estimates and fluctuate throughout the year."

He admitted that the statistics showed the economic downturn was "significantly affecting" young people, but said annual data from last year revealed that the proportion of young people who were studying had also reached record proportions at 79.7%.

The number of 16- to 18-year-olds out of work, training or education rose by 13,000 in just three months, the figures show. In March this year, there were 220,000 neets. The figure is now 233,000.

By June last year, 209,000 teenagers aged 16 to 18 were neets, 24,000 fewer than by June this year.

Brendan Barber, general secretary of the Trades Union Congress, said: "We cannot afford to lose another generation of young people to unemployment and underachievement.

"Tackling this crisis won't come cheap. We need more employers to take on apprentices and the government must ensure its guarantee of training or work for young people out of work continues to be well funded, as demand will be high.

"Neets are likely to have low skills and poor experience, so the training and work on offer must be meaningful. Otherwise it will just be a stopgap before further unemployment."

The Conservatives' shadow universities and skills secretary, David Willetts, said young people needed more apprenticeship opportunities and postgraduate places, and better careers advice.