A further influx of adult students is expected in a move to reduce benefit dependency.
The 680,000 people claiming jobseeker's allowance will be the first to experience a new system from the autumn which involves compulsory checks on how their skills compare with the needs of the local labour market. These will be followed by training, where appropriate, to increase their chances of finding work.
Ministers plan to extend the regime to other groups. Single parents on income support are likely to be forced into training once their children reach school age, affecting up to 470,000 people from 2010.
The move has renewed concerns about the increased use of colleges as compulsory places of learning.
The government policy paper, called Work Skills, also said people on incapacity benefit will be expected to retrain for a job that suits their abilities, if judged fit to work.
Nearly one in three unemployed people have no qualifications. And according to research for the Department for Work and Pensions, about half of jobseeker's allowance claimants believe they do not have the right skills to get work.
Martin Doel, the Association of Colleges' chief executive, said colleges are ready for the challenge of taking the extra students. He said: "We have ample evidence of colleges responding to the needs of the widest cross-section of students in their communities, including the long- and short-term unemployed."
Unemployed people are sceptical of the benefits of taking courses unless there is an immediate prospect of a job, researchers found.
The Government argues its policy will be a better deal for the taxpayer - with investment in training reducing the benefits burden.
The paper said: "It is not acceptable that a lack of skills should prevent someone claiming jobseeker's allowance from getting sustainable employment; nor that someone starting to claim incapacity benefit should expect to stay on that benefit instead of retraining and getting a job that reflects their abilities. Nor is it acceptable that a lone parent should wait until their youngest child turns 16 before they get ready to return to work."
The University and College Union said forcing more people to train would cause make life hard for lecturers accustomed to teaching people who had chosen to study. Already, compulsory education has increased in colleges, with 14- to 16-year-olds from schools attending part-time. It will increase further with the raising of the education and training leaving age to 18.
Paula Lanning, the union's head of communications and public affairs, said: "We are not in favour of people being forced into education. It's not something that makes life easier for the people who teach them. They should be there voluntarily, and the key issue is how to make the provision attractive for people in this situation.
"It's a diversion from the real issue of making the curriculum relevant and, in the case of unemployed people particularly, ensuring that colleges have the resources to do their outreach work for people who often are under pressure."
Colleges said they would work with the Government on the plans, but questioned where the funding would come from if large numbers of unemployed people were pushed into training.
Colleges face new age of compulsion
The prospect of mandatory training for people on benefits is the latest in a string of policy initiatives to increase the number of compulsory students in colleges.
Colleges are already preparing for an influx of teenagers following the decision to increase the education and training leaving age to 17 in 2013 and 18 in 2015.
This will bring an estimated 200,000 teenagers into the fold - with many opting to go directly to college. Others will choose to carry out government-recognised training programmes such as apprenticeships, which may also involve an element of college support.
The increased flexibility programme currently places 90,000 14- to 16- year-olds from schools in colleges part-time, primarily for vocational training to improve their motivation by providing an alternative to the academic route. These numbers continue to increase.
The number of compulsory students created by the new policy aimed at people on benefits is unknown. Whether they are deemed to need training will depend on the local employment market - meaning even those with degree-level qualifications could be made to train if they lack the right job-specific skills.