Earlier this month, a report from the Commons education and skills select committee predicted that schools would see spending rises of only 2 to 3 per cent in future years, instead of the 5 to 7 per cent they had become used to.

Last week, Gordon Brown won plaudits by renewing the Government’s commitment to education. He pledged to close the gap between the pound;5,000 per pupil to be spent in state schools in 2006-07 and the pound;8,000 per pupil spent in the independent sector.

“To improve the pupil:teacher ratios and the quality of our education, we should agree an objective for our country that stage by stage, adjusting for inflation, we raise average investment per pupil to today’s private school level,” the Chancellor said.

As a first step, capital spending on buildings and equipment will rise to private-school levels by 2011.

Mr Brown also said: “In private schools there is one teacher for every nine pupils, compared with one teacher for every 16 in state secondary schools...

“Our long-term aim should be to ensure for 100 per cent of our children the educational support now available to just 10 per cent.”

Seasoned observers of Brown budgets quickly spotted two important caveats, however. The Government refused to give itself a deadline to meet this pledge and the Chancellor did not commit himself to match future increases in private-school fees.

When the spin is stripped away, Mr Brown’s rhetoric amounts to nothing more or less than a promise to increase school funding per pupil faster than the rate of inflation. If independent school fees rise faster than inflation, the gap between funding in the state and private sectors could widen, even if the Government meets the letter of Mr Brown’s pledge.

His promise may be easier to keep as the number of school-age children is expected to fall by more than 6 per cent by 2013, giving an automatic boost of funds per pupil.

Barry Sheerman, Labour chair of the select committee, welcomed the Chancellor’s “reassuring” words, but said he would be pressing for a definite timescale.

“A lot of this may just be aspirational. Our job is to make sure we take this and pin himdown on it,” he said.

He said that if the goal were reached by 2011, it would mean increasing the percentage of money spent on education as a proportion of gross domestic product from 5.6 to more than7 per cent, pushing it above health.

Alissa Goodman, from the Institute for Fiscal Studies, calculated that closing the gap with today’s independent-sector spending would be costing the Chancellor an extra pound;17bn a year by 2011. If education spending as a percentage of the economy remained constant, it would take 16 years to achieve. But if Labour managed to match the level of spending increases in its first 11 years of office, the goal could be reached in seven years.

The cost of meeting the Chancellor’s pledge would increase further if parents who would otherwise have sent their children to private schools see the effects of higher spending and choose state education instead.

Further doubts were cast by the Conservatives on Labour’s spending promises .

They looked back at Tony Blair’s 2001 pledge to bring state school resources up to the level of the independent sector.

They said that since the Prime Minister made the commitment at that year’s Association of Teachers and Lecturers’ conference, the gap had actually widened from pound;2,020 to pound;3,000 per pupil.

A Department for Education and Skills source did not dispute the figures, but said: “No government has put more money into education than the current administration.

“There has been a 36 per cent real-terms increase in per pupil revenue funding since 1997-98, and the Chancellor’s Budget last week reaffirmed our commitment to a world-class education not just for the few, but for every child.”