And almost 2m are unable to go online at home, according to leading digital education charity, the E-Learning Foundation.
It also claims those from the poorest families are two-and-a-half-times less likely to have the internet at home than children from the richest homes.
The government would not comment on the findings.
The E-Learning Foundation, which works to ensure that all children have access to the internet and a computer at home, has analysed the latest government spending survey.
It found that while computer access is growing in better-off households, those from low-income families are being left behind.
'Get worse'It is warning that many of the UK's poorest children face being severely educationally disadvantaged by their lack of access to technology as a result.
In November more than half of teachers who took part in a survey for the Times Education Supplement said pupils without access to internet or a computer at home were hampered in their learning.
The foundation's chief executive, Valerie Thompson, said: "With so many children swamped with gifts from family and friends over the Christmas period it is important we reflect on the fact that millions of children live in poverty in this country.
"For those at school, this translates into very tangible disadvantages when it comes to completing homework, researching topics, independent learning, and communicating with teachers and classmates on the school learning platform.
"Without the use of a computer and the ability to go online at home the attainment gap that characterises children from low income families is simply going to get worse."
The Department for Education was not prepared to comment on the findings.