Nor does she hesitate when it comes to describing “good Plowden” and “bad Plowden” schools. In the first, while the focus is on the individual child,the teachers keep absolute control and discipline is good. In the second, teachers “lose their heads”. She remembers very distinctly seeing two boys sitting in the corner of a classroom, drawing a herring and giggling. “They weren’t working,” she says tartly.

She is sad to have lost her connection with a “good Plowden” school, Marlborough Primary in Chelsea, when her husband’s ill-health persuaded the couple to leave London and move full time to the white-painted Essex manor house they bought 50 years ago.

Now 86, Bridget Plowden sits in the drawing-room, a large open fire burning in the grate; faint bangs can be heard from a pheasant shoot in the background. And you sense the return of the restlessness from which she was suffering when Sir Edward Boyle picked her to chair the committee of inquiry into primary education 33 years ago. This wiry, energetic and highly intelligent woman, whose four children had left home, wanted something to do.

“I was fidgety,” she says, “and wanted some occupation beyond being a secretary and a typist. It was a very welcome opportunity. And, as I like children, it was particularly attractive.”

Now what was this formidable woman doing as a secretary? The daughter of Sir Herbert Richmond, an admiral and noted naval historian who ended up as Master of Downing College, Cambridge, she had spent much of her childhood on the move. Two years in Ceylon with a French governess were followed by three years at Downe House, a boarding school in Berkshire. When she started to study history at Bedford College, London, she discovered after two terms that her disrupted schooling had left her without the necessary qualifications in Latin and maths. She left to fill the gaps but was not then prepared to start her degree course all over again. She trained as a secretary instead.

Her one and only full-time job was as secretary in a boot factory in Kendal (“I knew somebody who owned K Boots”). She spent two years on her own in lodgings in Kendal, played the clarinet in the

K Boot orchestra, ran the Brownies, and then got married to Edwin Plowden,who has had a long and distinguished career in industry and public life.

Her own experience of state education was confined to the village schools in Shropshire and Essex that her children attended before going to boarding school. Her sons went to Eton, her daughters to convents. But she had been a juvenile magistrate before the Second World War and was, she says, “aware of some of the problems which affect the young”.

None the less, the appointment of an unknown woman with no previous track record in education to chair the committee of inquiry into primary schooling in 1963 was greeted with some surprise.

It had come about in the most establishme nt of ways. Sir Toby Weaver, then a senior official at the Department of Education and Science, is a cousin; Sir Edward Boyle, then Minister of Education, was a friend of her husband’s. Once he had met her, Sir Edward was in no doubt: “I’ve found the chairman I want and that’s it,” he told his startled officials.

She was an amateur chairing a committee of professiona ls, with expert advice from Her Majesty’s Inspectorate, notably the formidable Stella Duncan. But Biddy Plowden did not sit back and let the experts run the show. “She was very strong-minded and very clear-minded,” says Maurice Kogan, who was secretary to the committee. “She had strong control of the committee and the report and spent several days a week on it.”

For Lady Plowden, the three-and-a-half years she spent on the inquiry were hugely enjoyable. “It was very exciting: the first time I’d done anything in so wide a field,” she says. She stuck to her last, too, taking on many speaking engagements to spread the report’s message and convening an annual meeting of members to discuss progress with its implementation (always too slow, of course).

Once launched on her belated career as a member of the great and the good,the next 25 years were a whirl of activity. In education, she was a member of the Inner London Education Authority and of the 1974 inquiry into teachers’ pay, president of the Advisory Committee for the Education of Romany and other Travellers, of the Pre-School Playgroups Association, of the National Institute of Adult Continuing Education and of the College of Preceptors. She is still involved as a patron of Volunteer Reading Help and with an adult literacy scheme. Outside education, she has been chairman of the Independent Broadcasting Authority and president of Relate (formerly the National Marriage Guidance Council).

Her great and lasting achievement, however, remains the report on primary education. Much of it - the emphasis on parental involvement, positive discrimination, the abolition of streaming and corporal punishment - has become established practice. The expansion of nursery education was taken up by a young Margaret Thatcher and the aim - though not the method - is now common ground between the parties.

But it is the emphasis on child-centred, active learning that is most widely associated with Plowden by friend and foe alike. Lady Plowden is unapologetic about the thrust of the report, although she has many times had to correct the misapprehension that it advocated nothing but topic work and sloppiness. “We certainly do not deny the value of learning by description or the practice of skills and consolidation of knowledge, ” the report said clearly.

She remembers the sort of thing the committee was trying to get away from: a school she visited where all the children were sitting in rows doing an exercise at the same time from the blackboard.

“At the end of 40 minutes, two of them hadn’t finished the problem they were doing,” she says. “That’s one of the problems with formal education: if you’ve got a mixed bag of children, how do you stretch the most intelligent and not distress the slowest? Unless you can work at an individual pace, some will never have the satisfaction of finishing.

“It is possible to do,” she says firmly, “but I don’t know if you need exceptional teachers to do it.”

As I prepare to leave, the odour of sprouts suggests I am keeping her waiting for lunch. But she would rather stay to talk about education than eat. “Lunch is not one of my priorities,” she says. “Time stretches out before me.”