The number of people in Britain who do not have a job and would like one is 4.2m, twice the official tally of those unemployed, according to an analysis by the Trades Union Congress.
In addition, there are 829,000 people working part-time for the solely because they cannot get a full-time job.
The analysis “means that policies to deal with the recession are going to need to last longer than people are imagining”, said Richard Exell, senior policy officer at the TUC.
The TUC said its research, based on data from the Office for National Statistics’ monthly labour force survey, was a measure of ”labour market slack” rather than hidden unemployment.
The official total of unemployed people rose to 2.1m – or 6.7 per cent of the workforce – in the three months to the end of February, the highest figure since Labour came to power in May 1997.
Business leaders and economists expect unemployment to top 3m by this time next year, leaving 10 per cent of the working-age population without a job.
To count as unemployed under the internationally agreed definition recommended by the International Labour Organisation, people have to want a job but not have one, have looked for work in the last four weeks and be ready to start work in the next two weeks – or be waiting to start a job in the next two weeks.
But the labour force survey also studies people of working age who are “economically inactive” – outside the labour market for reasons including being retired, looking after a family, or suffering long-term sickness.
In the latest employment figures there were 7.8m working-age people who were economically inactive, and of these 2.1m said they wanted a job.
Mr Exell said: “The ILO definition of unemployment means there are plenty of people who do not have a job but still want one. For various reasons they may not have been looking recently, or may not be able to start work straight away, so they are classed as economically inactive even though they really want paid jobs.”
While official unemployment has been rising, the number of economically inactive people wanting jobs has remained stable in recent months – meaning that the combined total is increasing.
The TUC was pleased that the government set aside £3.1bn ($4.6bn) to shore up efforts to tackle unemployment in April’s Budget.
But it was less happy that Alistair Darling, the chancellor, rejected pleas for wage subsidies to help companies working short-time, and for a big increase in jobseekers’ allowance.