It is understood ministers want to adopt a method more closely based on international standards which could result in higher numbers of jobless.
The current system also excludes unemployed people younger than 18.
In opposition, Labour politicians, led by John Prescott, the party's deputy leader, complained that the published monthly headline figures underestimated the extent of unemployment, sometimes by millions.
Since then, government statisticians have reviewed methods and decided on a new measure which is likely to increase the numbers counted as unemployed by around 400,000.
This would mean the current 1.4m total becoming 1.8m by the new definition.
Statisticians do not go as far as backing Labour's more extravagant claims, but they do support the argument that official figures have understated the numbers able and willing to work but who cannot get a job.
How the sums have changed
In September 1975, the Labour government was attacked after unemployment reached a million for the first time.
Using the current system of accounting, revised many times by Conservative governments since 1979, that figure would have been just 884,100.
The changes implemented include:
October 1979
Downward adjustment to seasonal total
July 1981
Unemployed men over 60 on supplementary benefit for a year or more given option of long-term rate instead of signing on.
July 1982
Unemployment benefit taxed. Single parents encouraged to switch to supplementary benefit which was not taxed.
October 1982
Benefit claimants counted by computer rather than those registered for work at Jobcentres.
October 1982
Those seeking part-time jobs eliminated from count.
April 1983
Men aged 60 and over not entitled to benefit no longer made to register to receive National Insurance credits.
June 1983
School-leavers barred from claiming benefit until September in the year they leave.
July 1985
Payment of unemployment benefit in arrears.
June 1986
New method of calculating unemployment rate using larger denominator.
June to October 1986
Restart and availability for work tests tightened.
September 1988
Benefit denied to all 16 and 17-year-olds.
October 1988
Social Security Act changes conditions for short term benefits and puts some people over 55 on pensions instead of benefits.
September 1989
Claimants made to prove they are actively seeking work. Low wages no longer acceptable as reason for refusing a job.
September 1990
Unemployment benefit and income support ended for students.
April 1996
Unemployment benefit cut from 12 months to six months.
October 1996
Jobseeker's Allowance replaces income support and unemployment benefit. Cuts contributory benefit for 18 to 24-year-olds by 20%.
UK unemployment at 17-year low
(14 Jan 98 | UK)
Department for Education and Employment
Office for National Statistics
Employment Service
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