Only 45 pupils on free school meals (FSM) made it to Oxford or Cambridge universities in a single year, according to figures uncovered by the Conservatives.
The number is nearly half that of London's independent Westminster School, where an average of 82 pupils gain entry to Oxbridge each year.
Another private school, St Paul's Girls', also in London, produces the same number of successful Oxbridge applicants annually as the nation's entire cohort of FSM pupils, figures suggest.
The statistics were revealed in the answer to a parliamentary question from shadow schools secretary Michael Gove. They show how many 15-year- olds in receipt of FSM in 2002-03 progressed to higher education in 2006- 07.
Just 45 of the 81,100 pupils won places at Oxford or Cambridge, the figures show. Only 1 per cent of the pupils went on to study at one of the 20 elite Russell Group universities.
The statistics follow others uncovered by the Conservatives that show only 189 FSM pupils gained three A grades at A-level in 2007, of which 75 were boys. In the same year, Eton had 175 boys who achieved the same feat.
Mr Gove said the numbers showed the "true extent" of Labour's education failure.
"The very poorest pupils have been let down by a school system that simply is not good enough," he said. "Standards are falling, discipline problems are rife and headteachers are increasingly being micromanaged by Whitehall.
"A Conservative government will give every child the kind of education that is currently only available to the well-off: safe classrooms, talented and specialist teachers, access to the best curriculum and exams, and smaller schools where teachers know the children's names."
In response, schools minister Vernon Coaker initially claimed the Tories were using "misleading figures" in a bid to "do down" the achievements of young people because the statistics did not include those who took A- levels at further education colleges. But a Labour spokesman later conceded that Mr Coaker was incorrect.
The Conservatives accused Mr Coaker of "trying to hide the truth".
A Conservative spokesman said: "Vernon Coaker is trying to manipulate his own department's statistics. He is wrong to suggest that the free school meals figure does not include pupils who took their A-levels at further education colleges.
"As the parliamentary question clearly states, the figures are of pupils on free school meals at age 15 who then progressed to higher education by the age of 19.
"Whether they went to further education colleges in the intervening period is immaterial. And as the notes to the parliamentary question point out, the data `includes higher education level courses at English further education colleges'."
The spokesman added: "Coaker is trying to hide the truth, but there is no disguising government failure on education."
Crying foul on figures
This week has seen both Labour and the Conservatives firing accusations of foul play at one another over the use of figures.
Labour has listed examples of what they say is the Conservatives "twisting" statistics.
On Monday, Labour pointed out that the teenage pregnancy rate was 5.4 per cent, rather than the 54 per cent they had purported in a new report. The Tories, while acknowledging that the figure was incorrect, claimed this "made no difference at all".