The number of schools condemned as failing by inspectors rose sharply last year, David Bell, the chief inspector, will reveal next month.

His annual report will show that the Office for Standards in Education placed 24 per cent more schools in special measures during 20023 than it did in 20012.

Even more worryingly, the rise in failing school numbers has accelerated since September 2003. While the introduction of a new inspection framework had been seen as a cause, Mr Bell’s figures will raise fears of a deeper, more long-term trend of school failure.

Financial problems or teacher shortages have been cited as possible reasons for a drop in standards in some struggling schools. Many which failed their inspection had already been judged to have serious weaknesses.

The number of schools in England failing an inspection rose from 129 in 20012 to 160 last year. In 20012, 94 primary, 19 secondary, 10 special and six pupil-referral units failed. For 20023 the figures were 99, 35, 18 and eight. The total number in special measures at the end of the year, which had fallen steadily since 1998, rose from 272 to 282.

Mr Bell has already revealed that a further 46 schools failed an Ofsted inspection during the first half of the 2003 autumn term, a 35 per cent rise on the same period the previous year. In autumn 2002, 2.7 per cent of schools which had a routine inspection were failed, but that figure rose to 4.5 per cent in autumn 2003.

Now Ofsted is commissioning research to assess the impact of its inspections on the education system. Professor Pam Sammons of London university’s Institute of Education is in discussions with the agency about the project.

She pointed out the total number of schools in trouble had actually gone down, because there had been a drop in the number judged to have serious weaknesses, from 201 in 20012 to 163 last year. But a growing number appeared to have failed because they had not addressed those weaknesses.

“I would want to look at the reasons why schools are going into special measures,” she said. “It could be related to teacher shortages, with retention and recruitment problems making it difficult to raise standards, or it could be to do with funding difficulties.”

John Dunford, general secretary of the Secondary Heads’ Association, called for a review of the way inspectors were carrying out their work. It was not clear whether the rise was accidental or deliberate, he said.

“There is evidence of a variety of interpretations by inspectors which can be very unhelpful. It may well be that this was not intended,” he said.

Tim Collins, a Conservative party education spokesman, said ministers must investigate the apparent drop in standards.

“These figures are disappointing although it’s a little early to say they are alarming,” he said. “The long-term trend of improvement has at best halted or has started to reverse, maybe as a result of the funding crisis.”

The figures coincide with an online survey by the National Association of Head Teachers on the impact of school inspections since September. Of 31 schools inspected last term, 21 had been rated as having serious weaknesses or needing special measures.

David Hart, NAHT general secretary, said that he would be writing to David Bell. “Alarm bells must be ringing,” he said.