Tens of thousands of unemployed people have been made to work without pay under threat of having their benefits removed for at least 13 weeks, according to the latest government figures.

The first set of statistics on the government's mandatory work activity (MWA) programme reveals that from when the scheme started in May 2011 until November, 24,010 jobseekers were referred to work for four weeks unpaid for 30 hours a week.

Under the scheme – the first of its kind in the UK – jobcentre managers have the power to make unemployed people do a month's work experience at charities, government offices or high-street chains if they feel claimants "fail to demonstrate the focus and discipline necessary to seek out, secure and retain employment opportunities". If they do not take part, claimants have their benefits removed for 13 weeks. A second failure to take part means benefits are removed for six months.

In a separate scheme, managers can also ask jobseekers to take up unpaid work experience (WE) for eight weeks. However, under this programme, people can refuse to do the work or pull out within the first week without having benefits docked. Figures for the programme reveal that 34,200 jobseekers undertook such placements from January until November 2011.

The figures show a wide variance between gender and race groups entered into the two schemes. Of those being referred to the mandatory scheme, 75% (18,000) were male, while 66% were male in the non-mandatory WE scheme.

Figures for ethnicity reveal that 24% of those being forced to do work experience were from minorities compared to only 13% on the voluntary WE scheme.

The large differences raise questions about the choices being made by jobcentre claims managers after a Department for Work and Pensions (DWP) insider told the Guardian they could see no statistical reason for the a racial variance.

There has been exponential growth in the number of people being sent on mandatory "workfare" placements since they were introduced in May. In the three months from September referrals doubled, and by November, the last month for which figures were released, there were more people being sent to mandatory placements (8,100) than starting a WE placement (6,600) throughout the whole of the UK.

In response to questions about the figures, the DWP warned that the number of those referred for mandatory work would not precisely equate with those who were actually starting such placements, for which figures were not currently available.

"Not every claimant referred to mandatory work activity starts on the scheme," the department said. "This can be for a variety of reasons; for example, they may cease to claim jobseeker's allowance before the start of their placement, their circumstances may change, or they may remain on jobseeker's allowance and fail to start a placement."

The department added that the figures for the two schemes were not directly comparable and they had carried out a full equalities impact assessment.

"Mandatory work activity and work experience are two different schemes with different aims and referral criteria. The department does not make direct comparisons between the schemes.

"Claimants are referred to mandatory work activity on the basis of suitability for the scheme, regardless of their gender and ethnicity. A full equality impact assessment has been completed with regard to mandatory work activity. As set out in this equality impact assessment, a higher proportion of males claim jobseeker's allowance compared with females. These early figures suggest that the proportion of claimants referred to mandatory work activity who are male is slightly lower than predicted in the equality impact assessment."

The department also said it had plans to introduce a three-year sanction for those who failed to complete MWA for a third time under welfare reforms currently making their way through parliament.

"Ensuring participation in mandatory work activity will be critical to help some claimants prepare for work. Failure to complete a mandatory work activity placement without good cause will result in the sanction of jobseeker's allowance for three months. This will rise to six months for a second breach. Subject to the passage of the welfare reform bill, a three-year fixed sanction will apply for a third violation.

The shadow employment minister, Stephen Timms, said: "With unemployment at its highest rate since 1995 and long-term youth unemployment doubling in the last year, it is absolutely clear that this government's welfare-to-work programmes are not doing the job … Complacent ministers simply must do more to get people into work."