Almost 17 million adults have basic maths skills that are no better than children aged nine to 11, as numeracy levels worsen, Government-commissioned research reveals.
Over five million people are struggling with simple reading and writing, it shows.
The latest Skills for Life survey questioned more than 7,000 16-65-year-olds in England to examine literacy and numeracy levels. The findings reveal that many adults still have maths and English skills similar to those expected of primary school children.
Campaigners warned that there are "far too many" people with poor basic skills, and more needs to be done for them.
In total 16.8 million adults (49.1%) have numeracy skills at Entry Level 3 or below. This level is equivalent to the achievement expected of a child aged nine to 11. Adults with skills below this level would struggle to pay household bills, or understand price labels on pre-packaged food.
This is up on 2003, the last time the survey was conducted, when 14.9 million adults had numeracy skills at Entry Level 3 or below. In literacy, 5.1 million adults (14.9%) were at Entry Level 3 or below, down slightly from 2003, when the figure stood at 5.2 million.
The survey also reveals that millions of adults are no better at maths and English than five to seven-year-olds. In total, 2.3 million people in England were found to be at Entry Level 1 or below - the level of attainment for five to seven-year-olds in numeracy, while 1.7 million (5%) were at this stage for literacy.
Carol Taylor, director for research and development at the National Institute of Adult Continuing Education (Niace), said: "We have far too many people with very poor basic skills in this country and the system isn't working for them.
"Put simply, around one in six of the adult population has difficulty with aspects of reading and writing which means they are seriously disadvantaged as employees, citizens and parents. And around one in four of the adult population struggle with the basics of numeracy, a skill which can have a greater impact on life chances than literacy.
"This is why we're calling for a specific challenge fund to help those with the lowest skills."