A drive to boost adult literacy and numeracy is failing to offer improved teaching and doubts remain over the likely cost, a report by MPs says.
A campaign urged adults to tackle their learning 'gremlins'
Up to 12 million working UK adults have the literacy skills expected of a primary school child, the Public Accounts Committee says.
It raises doubts about the Skills for Life plan, which aims to help 2.5 million adults in England by 2010.
The Department for Education says it is too soon to assess the strategy.
Skills for Life was set up in 2001.
The Public Accounts Committee says it does look set to achieve its aim but there are concerns about the quality of education on offer.
It says no-one knows how much it would cost to complete the strategy.
It cites the "widespread weaknesses" found in an extensive quality review by Ofsted and the Adult Learning Inspectorate.
And it goes on to say that people in the greatest need are receiving the worst provision.
It states: "The quality of provision for adults with literacy and numeracy needs is still too low."
Chairman Edward Leigh said: "The low level of literacy and numeracy in the adult population is bad for national productivity and bad for those individuals who may struggle to cope with work and daily living.
"The Department has the laudable long-term aim... of making sure that England has one of the best literacy and numeracy rates in the world. But the task is a huge one."
The government has spent £3.7bn since 2001 on the scheme.
Mr Leigh said: "No-one knows exactly how much more money will be needed from 2006 to 2010: on current patterns, perhaps more than £2bn. The department must harden up its estimates of future costs."
The report says there are up 12 million people holding down jobs with literacy skills and up to 16 million with numeracy skills at the level expected of children leaving primary school.
It says the Department for Education needs to work on reaching those whose skills could benefit from improving.