In 2009, I wrote a history of Tony Blair’s education reforms with my University of Cambridge colleagues, John MacBeath and Maurice Galton. With the Gordon Brown government having just a year to go, it was a moment when key players in education policymaking were remarkably candid and willing to discuss their work of recent years with us.

Theresa May’s recent disinterment of grammar schools prompted me to look at our interview transcripts again, and particularly at what four previous education secretaries had to say on the subject.

Their political experiences were very different and, in their way, tell us something about how education has been treated politically over the years. Kenneth Baker, for example, remembered being amazed that, instead of giving him a list of things to do, Margaret Thatcher had said: “Go away, look at the problems, and come back in a month’s time and let me know what you think.”

Estelle Morris, the only former comprehensive teacher to have held the role, worried that no one responsible for reforms in Blair’s wider government understood the demands of teaching. And Michael Gove, then shadow education secretary, said that the critical question for him was: “Were we giving young people the same degree of opportunity that other countries, which were comparably as well off, do in theirs?”

Slipping down the agenda

The debate on how education reform might be delivered - and improved results delivered for every child - crackles through the transcripts, but there is one principle that none of my interviewees questioned. All saw quality education for all students as a top-priority enterprise for the country. And not one referred to grammar schools. Not one.

This is not an exercise in nostalgia. England has experienced 30 years of education reform, with wildly varying swings in policy and funding, but Blair’s 1997 decision to make education a top priority (in his famous “Education, education, education” speech) gave the sector a massive political boost and, for the two decades since, the trajectory of its importance to policymakers has been only upwards. Until now.

May’s grammar school initiative calls into question all previous assumptions about education’s place in society.

There is absolutely no evidence that grammar schools will improve education for all young people or improve social mobility. Given Gove’s dismissal of experts during the Brexit campaign, I don’t know whether he felt any sense of hypocrisy when he urged May to adopt evidence-based policymaking, but it is a sign of how far things have moved.

Let’s take the conclusions of Pisa (the Programme for International Student Assessment) as an example - and it is a timely one, since the findings from the 2015 round of the Organisation for Economic Cooperation and Development (OECD) tests will be published in December. Until recently, Pisa has been treated with respect verging on the holy by UK governments. Previous education secretaries have hosted Pisa’s launches and engaged with its findings. OECD education director Andreas Schleicher’s recent comments that selection favoured social background over academic potential drew on longstanding Pisa conclusions. Indeed, warning against the damaging effects of “early tracking”, as the OECD calls it, goes back as far as the first Pisa.

Yet neither current education secretary Justine Greening nor May show any signs of being aware of these findings. Instead, the Department for Education’s response was simply to ignore Schleicher and say that new and existing selective schools would prioritise the admission of disadvantaged pupils.

The upward trajectory of education as a policy priority has come to a juddering halt

The Brexit campaign heralded the emergence of what some describe as “post-truth politics”. It is clear from May’s grammar school initiative that we are now in the era of “post-truth education”. Indeed, one effect of Brexit seems to be that where the government considers international evidence on education inconvenient, it will be derided.

And there is one key feature of the evidence that the government will find highly inconvenient. A common feature of the top-performing countries in Pisa is that there is cross-party, parent and teaching union consensus on the importance of education as a public service and its key features. In Finland, a consistent top performer, those features are described as cornerstones of the education system, and they certainly don’t include selection.

The implications of pulling up the drawbridge on evidence go even wider than that. If the Brexit referendum was triggered by the need to sort out internal Conservative Party management issues, then the reintroduction of grammar schools comes from the same political mindset. It is a useful distraction from the emerging unpalatable truth of the post-Brexit negotiations. A dead cat, as David Cameron’s former spin doctor Lynton Crosby would describe it, has been flung on the table to divert the public’s attention.

In short, May’s decision to introduce something as divisive as selection is a sign that the upward trajectory of education as a policy priority has been brought to a juddering halt. Education is now more important as a tool of post-truth politics than as a country-unifying consensus.

Labour’s campaign against selection will be successful if it makes allies with opponents from other parties and organisations. An evidence-based education system must be the ultimate strategic goal for all who understand that an inward-looking education system informed by post-Brexit politics will fail young people and society.

John Bangs is honorary visiting fellow at the University of Cambridge and a former head of education at the NUT teaching union