Never believe what you write in the newspapers," the late Malcolm Muggeridge said to a young journalist. I do not know whether Daily Mail journalists believe what they write, but they should certainly be sceptical about it.
The Daily Mail is a phenomenon, perhaps the most important of our age. In the 1970s, trade unions got reverential treatment from the Left simply because they were the most successful left-wing institutions. Now, as all other right-wing institutions and habits of thought fall into decline, the Mail sails on.
Tony Blair may soar in the polls, Labour may acquire a reputation for economic competence, London may buzz with the ideas of left-wing think-tanks, but the circulation and influence of the right-wing press is unabated.
So when the Daily Mail splashes that "Britain has the worst schools in Europe", as it did last week, we should take heed.
This story was based on a report from the Organisation for Economic Co-operation and Development (OECD) to the effect that "literacy levels among young Britons are among the worst in the industrialised world, with one in three lacking the skills to cope with everyday life".
This looks impressive and categorical, but it means absolutely nothing. I have before me a table from that OECD report, showing the UK top of 18 countries for literacy (that is, enough to cope with the "complex demands" of everyday life) among 46 to 65-year-olds. If that is a true reflection of reality, we should cheer for grammar schools. But it isn't true.
The table records levels of literacy among those 46 to 65-year-olds who had completed "only upper secondary education". In other words, we came top because of our failings: we got so few people through to A-levels that only the brightest could make it. And most of them didn't go to university. Any teacher from the 1950s and 1960s will tell you that pupils who tookA-levels but didn't go to university were awesomely bright, and that this was a waste of talent.
It was inevitable that, some 30 to 50 years later, a high proportion of them should, in an international survey, show up as literate.
Now, the reverse applies. By international standards, the UK allows a high proportion of its young people to "complete secondary education" (certainly higher than Portugal which came above us in the OECD tables); from this larger and more varied cohort, we inevitably slip down the literacy table.
Almost all educational statistics should be treated with suspicion. Their significance depends on what is being measured; and this is never quite what it seems.
The widespread belief that a significant proportion of recently-educated British adults is illiterate (I have seen anything from 15 to 33 per cent quoted) is simply wrong. Illiteracy as most people understand it - you cannot read a word or sign your own name - is almost extinct.
What is meant is that people cannot read tax forms or understand train timetables. But on such criteria, most of us would count as illiterate or innumerate. Who, in Britain, would sensibly answer that a train scheduled to leave at 5pm and to arrive at its destination at 6pm will take one hour? Anybody who answers "Eighty minutes (maybe)" is much smarter than somebody who gives what OECD examiners would doubtless consider the"correct" answer.
Illiteracy is no worse here than in any other Western country. Nor is it significantly worse than it was 50 years ago. The panic is got up by people - adult literacy campaigners, teachers' unions, secretaries of state for education - who want to get money out of the Treasury. It doesn't mean that it's wrong to spend more on education, and it doesn't mean that I believe what I write in the papers.
Peter Wilby is editor of the 'New Statesman'