“These figures are likely to undercount the total numbers of problematic drug users and alcohol misusers in the benefit system, as people with another medical condition or disability with drug use or alcohol misuse as a secondary factor will not be included,” the paper said.
The total number of people claiming DLA is now 3.2 million, up from 1.1 million in 1992 when it was introduced.
Iain Duncan Smith, the Work and Pensions Secretary, has said that lax checks have allowed many undeserving people to claim the benefit, and promised to overhaul it.
The DWP estimates that £630 million a year is paid to DLA recipients who do not deserve it since their condition has improved since they qualified for the benefit. Another £190 million due to people whose conditions have worsened does unclaimed.
Mr Duncan Smith has said he will replace DLA with a new benefit called Personal Independence Payment (Pip) which will have tighter criteria and a simpler approval system.
An official DWP “impact assessment” of the plans, released earlier this year, reveals the change will cut benefit payments by £2.24 billion annually – and lead to about 500,000 fewer claimants.
Critics including some claimants have said that the Coalition’s welfare changes are unfair, but Mr Duncan Smith said the latest figures showed why reform is needed.
DLA is “not working as it stands,” he said. “What troubles me most is the chaotic structure of the current system.”