David Bell, the Department for Education and Skills' permanent secretary, said: "It is going to get tighter. I don't think there is any doubt about that."
He was appearing before MPs and responding to a question about what should be made of the mixed messages coming from the Government over education spending.
In March the Chancellor won plaudits for pledging to close the gap between the annual pound;5,000 per pupil spent in state schools and the pound;8,000 per pupil in the independent sector.
But there was no deadline on the commitment, and last week he painted a much bleaker picture. The Chancellor said the next public-sector pay deals would be based on three-year settlements limited to 2 per cent.
Asked whether Mr Brown had been misleading in suggesting the gap with the independent sector would be closed, Mr Bell said the Chancellor had been "laying out an aspiration".
Stephen Williams, Liberal Democrat, asked about the Institute for Fiscal Studies prediction that the review would lead to the annual spending increases under Labour falling from 4.6 to 3.4 per cent.
Mr Bell replied: "We recognise that the context might be tougher than it has been previously and that requires us to look very carefully at the priorities that we have.
"We do accept that the situation might be different in the future and we really do have to drill down hard on priorities."
Barry Sheerman, the Labour chairman of the committee, said education had now dropped to fourth in the annual spending increase league table, behind health, criminal justice and transport.
But Mr Bell said it was important to acknowledge the "huge investment" made since 1997 and the need for his department to use that money efficiently.
Meanwhile, it has emerged that the DfES had pound;468 million left unspent at the end of 20056, representing 1.5 per cent of its overall budget. The department said the majority of the underspend was made of capital funding already committed to local authorities and schools, that would be spent during the current financial year.