Alastair Wells, head of information and communications technology at The Netherhall School in Cambridge, said a solution might be to concentrate resources on those pupils who do not have home use of PCs.

In a lecture at the British Education and Training Technology exhibition in London, he suggested restricting the use of the technology at lunch time and after school to those pupils who do not have access to PCs at home.

The increased use of information technology in the curriculum and demands from pupils for e-mail were the major reasons for the soaring demand for computer time in schools, he said.

E-mail on demand only

His school had estimated that giving every one of its 1,400 pupils a personal e-mail address would mean they would have just 2.4 seconds a day each to make use of it. Consequently, addresses were given only to those who asked for them.

Mr Wells said the government's proposal to put £230m of National Lottery money into training teachers to use the technology would only exacerbate the problem.

"Putting two litres of water into a baby's bottle will not work," he said.

A pupil questionnaire carried out at The Netherhall School found that 75% of the pupils had access at home to computers that were less than two years old - broadly in line with the national average.