It’s that time of year again. In just over three weeks it will be the moment of reckoning for this year’s A-level candidates as the results land through the letter box. There will be whoops and cheers and the inevitable gnashing of teeth. Agonised phone calls will follow to university clearing.

And it will be the same schools who triumph again in the league tables. In the independent sector, St Paul’s girls’ school, London, and Westminster; in the state, the Latymer in north London and the Tiffin school, Kingston, both grammar schools. All beacons of excellence. And all very predictable.

But last week, something quite unpredictable happened. For the first time a teaching union voted in favour of selection. Peter Morris, a leading union official from the Professional Association of Teachers (PAT), persuaded his colleagues to call for the return of grammar schools. It is as if an old-style army major had barked that the army needed to embrace pacifism.

Ever since Anthony Crosland, then education secretary, vowed four decades back to “smash every f***** grammar school in the country”, it has been an article of faith for educationalists that if you support grammars you may as well send nippers up chimneys. Even Margaret Thatcher did not dare reverse the Shirley Williams revolution that all but ended selection in secondary education. Now only 164 grammars remain in England.

“This is a plea for honesty,” Morris explains. “We have selection anyway: look at Cherie (Blair) taxi-ing her son across London.” (A swipe at “faith” schools such as the Oratory in west London, which the Blair’s sons attended.)

Like many advocates of selection, Morris, who teaches near Swansea, believes that grammars enabled children from humble stock to compete with public school sorts. The reality of the decline of grammars means that private schools actually send a higher proportion of pupils to elite universities than 30 years ago when schools such as Manchester grammar were in their prime.

As far as Chris Woodhead, a former chief inspector of schools, is concerned, this PAT resolution is a welcome step — if a long time in coming. “Any government that is serious about raising educational standards and helping disadvantaged children must realise that grammar schools are the most efficient agent of social inclusion we have ever had,” he says.

A report from the London School of Economics (LSE) published last month showed that the decline of grammar schools had helped deepen class divisions, effectively kicking the ladder away from bright children. The LSE study found a link between income and educational achievement. Poorer families are priced out of the best state schools because of inflated house prices in the schools’ catchment areas and they cannot afford to attend private schools, which have filled the academic vacuum left by grammar schools.

A tranche of Labour politicians attended grammar schools, including Baroness Amos, Robin Cook and Peter Mandelson. So did Lord Bell, Mick Jagger, Victoria Wood and the new Doctor Who, David Tennant, to name but a few.

The conference vote puts pressure on Ruth Kelly, the education secretary, who says Britain’s lack of social mobility is her chief target. However, despite the evidence, government policy remains opposed to academic selection.

As a spokesman for the Department for Education and Skills commented last week: “The government does not support academic selection at 11 and does not wish to see it extended. Where selection exists, the government believes in local decision-making as to whether it should continue, and has put in place mechanisms to allow this to happen.” It has excluded the remaining grammars from plans to allow successful schools to expand more easily. Meanwhile, Northern Ireland is set to abolish its grammar schools, although the majority of parents canvassed wished to retain them.

Yet Labour circles do not present a united front on the subject of selection. Last week the pro-grammar lobby had good reason to celebrate — while quietly lamenting that little will change for the moment. Stephen Pollard is a former research officer for the Fabian society and member of a think tank, Centre for the New Europe. He was the co-author with Andrew Adonis, now Lord Adonis, of a study of social mobility, A Class Act, published in 1998. It argued that the dearth of grammar schools had made Britain more class- ridden than ever. “It never crossed my mind that that this resolution would be voted in,” says Pollard. “I thought this teacher (Morris) was a renegade. It breaks a log jam if one of the unions has endorsed grammar schools. It shows the people who are in favour of selection are not ludicrous.”

He wants more transparency in education and less wordplay. “This government finds it difficult to use the word selective, but it is happy to talk about specialist schools. I can see the semantic difference but what’s the difference for practical reasons?”

He is in favour of Labour expanding its specialist schools, including city academies. “I think we are moving to grammar schools by stealth, by the back door. My argument is, why not have them by the front door?”

Morris agrees. By 2010 ministers will be doling out hefty grants to schools with a specialism if they can also find funding from the private sector. “Why just encourage one specialism?” asks Morris. “Why not say to schools you can have several?” Grammar schools, in fact, by the front door.