Education Secretary Charles Clarke, who is on record as saying he is considering the impact of selection on academic standards, had asked the Office for Standards in Education to produce the report on the county which has the most grammar schools in the country.

Mr Clarke has said he has no plans to launch an “ideological” attack on the 11-plus.

But this week’s report may give him ammunition to take action on standards grounds.

It reveals that fewer schools in Kent (13.1 per cent) were judged “very good” in inspections than nationally (16.5 per cent). Its schools were also “substantially” more likely to require special measures or to have serious weaknesses.

The county ranked five out of seven comparable authorities in terms of the proportion of 18-year-olds going on to higher education.

And on results, the proportion of schools considered to be low-achieving was far higher than nationally. However, the report acknowledges this probably reflects the high number of secondary modern schools.

A spokesman for Mr Clarke would not say what action the Education Secretary would take. “It is up to local parents to decide the future of selective admissions at existing grammar schools. Any change would require legislation.”