The boys’ comprehensive occupies the run-down former stately home Hare Hall, a grade II listed building in large grounds, located in what the chairman of governors calls London’s “leafy suburbs”.

In 75 years, the Essex school has had just five headteachers. This year 42 per cent of its boys got five or more good GCSEs. Fewer than one in six qualifies for free school meals, parents are highly supportive and truancy is below average.

Yet it is failing. It has been on special measures since its inspection 12 months ago. And Mark Morrall, the new headteacher, is in no doubt the Office for Standards in Education got it “absolutely right”.

“Time and time again the report says the kids were being responsive but the diet the teachers were offering was appalling, ” he says. “The kids knew how to behave but the teachers had become complacent. ”

Royal Liberty is one of a handful of schools which occupy something of an OFSTED grey area - schools with decent results which disguise the fact they are failing their pupils.

And it is an extreme example of a much wider group of “coasting” schools which will find it increasingly difficult in 1998 to hide behind their GCSE pass rates.

Underscoring the line taken in Labour’s White Paper in July last year, school standards minister Stephen Byers, told a recent Industrial Society conference: “Perhaps 40 or 50 per cent of schools are just coasting, getting by but able to do a lot better. It’s those schools which will lead to a quantum leap in the level of achievement.”

That shift in focus is endorsed by OFSTED, whose chief inspector, Chris Woodhead, was involved in drafting the White Paper. Next month, OFSTED plans to send every school in the country information that compares their results with those of similar schools.

OFSTED says it has always judged schools against rigid criteria and will fail any school that does not meet them, regardless of results. But it acknowledges Royal Liberty does not fit the usual mould for failing schools, which to date have overwhelmingly been found in urban or inner-city areas.

Its March 1997 publication, From Failure to Success, described a weak secondary as typically having bad GCSE results, poor behaviour and attendance, and high exclusion rates.

Royal Liberty, by contrast, has had creditable results for boys throughout the 1990s, even if to call it coasting would be generous. Pre-inspection it averaged 27 per cent for five good passes - 1996‘s 28 per cent was seven points below the national average for comprehensive boys. But the head reckons that was 10 points below what the boys were capable of. Last year’s 42 per cent is the highest of any school on special measures, and the previous year it ranked among the top half dozen.

In other words, pupils have done well in spite of the teaching, which in almost half the lessons seen by OFSTED was less than satisfactory.

“Teachers hadn’t sharpened up their professional skills,” Mr Morrall says.“Schemes of work were not in place in all subjects. The notion of a variety of teaching styles was not evident. It was very much eyes down and get on with your work.” But what was obvious to him from his experience of failing schools was not obvious to others.

Governors were “devastated” by the OFSTED verdict, says their chairman Ruth Laws. Parents organised a 300-strong meeting to tell OFSTED it had got it wrong. The local authority, Havering, was more realistic about its first failing school. The former head took early retirement.

Mr Morrall, former deputy head at Phoenix school in Hammersmith, says there are distinct similarities with his old school, the London comprehensive fted by Labour as an example of a failing inner-city school successfully relaunched.

“Middle management didn’t really exist, ” he said. “There was no party line, so different signals confused staff. There was missing infrastructure. Teachers were not used to being observed or getting structured feedback.”

Royal Liberty is already a changed school, and hopes greater transformation lies ahead. Key new senior appointments have been made. A lottery bid to the Heritage Fund for a large-scale revamp of the site (any changes need English Heritage approval) is being prepared.

Mr Morrall believes, with appropriate loyalty, that his school is a sleeping giant. “Once we get through this difficult period we will be a showpiece for the authority,” he predicts.