Unemployment could be as high as 6.3 million in the UK if a different counting measure was used, highlighting the true scale of joblessness, according to a new report.
The TUC said the higher figure - more than twice the official total - was revealed using an American measure, which includes people in part-time jobs because they cannot find full-time work and recent redundancies.
The jobless total increased to 2.68 million last month and is expected to rise again when new figures are published by the Office for National Statistics on Wednesday.
But the TUC study suggested the actual number of unemployed people in the UK could be 6.3 million, which would be higher than any point since the early 1990s.
Under-employment, which counts those doing temporary or part-time jobs because they cannot find permanent, full-time work, has risen to a record 1.9 million, according to the research.
The TUC said temporary jobs were better than unemployment, but added that they tended to be low paid, insecure and offered little or no career prospects.
Officials called on the Government to acknowledge the scale of the jobs "crisis" rather than repeat the "ill-informed" claim that there were plenty of jobs available.
TUC general secretary Brendan Barber said: "The headline unemployment figures are bad enough, but the true scale of joblessness is even worse. Over six million people are either out of work or under-employed. Tackling this crisis should be the Government's number one priority.
"Our jobs crisis is not confined to those out of work. Nearly two million people are being forced to take low-paid, insecure, short hours jobs because of the lack of proper full-time employment. This means people are taking home much less pay, which is putting a real strain on family budgets.
"When ministers say there are plenty of jobs out there, they are ignoring the sheer numbers of people looking for work, as well as the suitability and location of the jobs available.
"Rather than seek to blame unemployed people for being out of work, the Government should start helping them by putting proper resources into employment schemes.
"Unless we get people back into decent jobs and wages growing in line with prices again, we will not secure a sustainable economic recovery nor get the deficit down."
The report followed a study by the Chartered Institute of Personnel and Development which showed that job prospects are set to worsen in the coming months as firms make workers redundant.
A survey of 1,000 employers also revealed a further widening of a North-South divide in the jobs market.
A Department for Work and Pensions spokesman said: "We firmly believe that being in some form of employment is better than being out of work.
"It is important that people are taking those first steps into employment through part-time work or jobs in different sectors as it provides vital experience and skills that employers will look for when the economy and labour market improve.
"The current climate is tough for jobseekers, but we also want people to know that there are jobs out there, with around 463,000 vacancies in the economy and with Jobcentre Plus adding on average 10,000 jobs to its books every working day."
This week's figures are expected to show the eighth consecutive month of rising unemployment, the IPPR think tank predicted, adding that unemployment has risen by a million since the recession began four years ago.
There are 600,000 more people working part-time who say they want to work full-time, compared to three years ago, said the organisation.
Graeme Cooke, IPPR Associate Director, said: "Every month that goes by, the urgent need for the new Youth Contract continues to grow. It is now almost a year since the Future Jobs Fund stopped giving young people a job guarantee after a year of unemployment.
"The next priority should be areas of the country experiencing the combination of both high unemployment and a low number of vacancies, while the prospects of those over 50 and unemployed for more than a year are also of serious concern.
"The longer someone is unemployed, the less likely they are to ever return to work. Being out of work for more than a year can have a scarring effect, making it harder to get a job as well as having a negative impact on one's health and well-being. This means that even when employment starts to pick up again, they will find it hard to compete with other jobseekers and could find themselves permanently shut out of the jobs market.
"The Government should guarantee everyone who has been unemployed for more than a year a job at the minimum wage in local government or the voluntary sector, but with that right should come the responsibility to take that job or risk losing their benefits."
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