"Significant action" needs to be taken as the UK's young people are falling behind the rest of the world in basic literacy and numeracy skills, it has been revealed.
Their skills are among the lowest in the developed world, and are no better than those of their grandparents, according to a major international study.
Overall, in England, young people came 22nd for literacy and 21st for numeracy out of 24 countries, trailing behind countries such as Japan, Finland and the Netherlands.
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Those in the same age group in Northern Ireland did slightly better.
The Organisation for Economic Co-operation and Development (OECD) warned that despite facing a tougher labour market, the UK's young people have skills similar to those who are retiring from the workplace.
The report, by the OECD warns that the UK needs to take significant action to boost the basic skills of the nation's young people.
The 460-page study is based on the first ever survey of the literacy, numeracy and problem-solving at work skills of 16 to 65-year-olds in 24 countries, with almost 9,000 people taking part in England and Northern Ireland to make up the UK results.
The findings showed that England and Northern Ireland have some of the highest proportions of adults scoring no higher than Level 1 in literacy and numeracy - the lowest level on the OECD's scale.
This suggests that their skills in the basics are no better than that of a 10-year-old.
In total, almost one in four adults (24.1%) - around 8.5 million people - scored at or below Level 1 in numeracy, compared with an OECD average of 19%. This meant that they can only do very basic sums.
In the literacy test, 16.4%, around 5.8 million people, scored the lowest level, compared with an OECE average of 15.5%. This meant they could read simple texts on familiar topics.
It puts the UK behind many other countries, including Japan, Finland and the Netherlands.
The OECD's report found that there was little difference between the basic skills of younger and older generations in England and Northern Ireland.
"Although young people in these countries are entering a much more demanding labour market, they are not much better equipped with literacy and numeracy skills than those who are retiring," a country note for the UK says.
It concludes: "The implication for England and Northern Ireland is that the stock of skills available to them is bound to decline over the next decades unless significant action is taken to improve skills proficiency among young people.
In England alone, those aged 55 to 65 did better than 16-24-year-olds in both of these tests, the OECD found.
The figures show that the average literacy score for 55-65-year-olds in England and Northern Ireland together was 265. This was one of the higher averages and put the UK above many countries.
But the average literacy score for 16 to 24-year-olds was virtually the same at 265.7, leaving the UK behind nations including Canada, France and Germany.
There was a similar picture for numeracy.
It suggests that while the basic skills of the working population in other countries has improved, in the UK it has remained static.
The figures come amid a rise in recent decades in the numbers of people staying in education and gaining more qualifications.
Andreas Schleicher, the OECD's deputy director for education and skills, said that basic skills are "the foundation, on which everything else is built".
"What we have is a snapshot of adults today," he said.
"When you look at this snapshot you do have to conclude that these young people are not any better skilled when it comes to those foundation skills than people in the older generation. And, more importantly, young people in the UK lack considerably behind their peers in other countries when it comes to those foundation skills."
Skills Minister Matthew Hancock said: "This shocking report shows England has some of the least literate and numerate young adults in the developed world.
"These are Labour's children, educated under a Labour government and force-fed a diet of dumbing down and low expectations."