How do you think we got comprehensive schools?” the hapless Jim Hacker was asked in a recent re-run of the Westminster comedy Yes Minister. Was it what parents wanted? Was it what the Government wanted? No, it was what the National Union of Teachers wanted.

While Sir Humphrey’s historical accuracy may be questioned, his description of policy formulation is more likely to elicit a hollow laugh today from the teacher unions after 17 years of Tory government.

Legislation to curb union powers and the decline of the nation’s manufacturing industries have seen membership drop from 13.2 million (in 1980) to 8.2 million today, with the actors’ union Equity having more people on its books than the National Union of Miners.

Teachers, however, buck the trend. Their unions claim growth and, according to Eamonn O’Kane, deputy general secretary of the National Association of Schoolmasters Union of Women Teachers, they still exert power.

They do so, however, in a very different world from the one Bernard Donoghue, former director of the Downing Street Policy Unit, inhabited in the 1970s. He later wrote that education policy was then conducted by the local authorities and the teacher unions, with the Department for Education being little more than a post box between them.

Since then, legislation has vastly increased the powers of the Education Secretary, and other functions and decisions are now made by a multiplicity of quangos.

Teachers did recently display industrial muscle. The national curriculum and tests boycott which led to the Dearing review and the slimming down of the curriculum has been called the greatest grassroots-inspired rebellion against the Government since the poll-tax revolt.

It was the NASUWT’s victory in the High Court, when the boycott was unsuccessfully challenged by the London borough of Wandsworth, that marked a change in the fortunes of the teacher unions (and did the NASUWT a power of good). It put paid to John Patten’s ministerial career and the unions enjoy much better relations with Gillian Shephard, a more teacher-friendly Education Secretary.

It may not be back to the old beer-and-sandwiches days - rather PG Tips and custard creams - but the teacher associations are regularly invited to the Department for Education and Employment and Mrs Shephard’s office will telephone the union leaders before a major announcement is made.

Whether they are listened to is a different matter. And if NASUWT general secretary Nigel de Gruchy’s fears are justified, it is the wrong door that has been opened.

“Ministers will always see us. The same applies to Anthea Millett [chief executive of the Teacher Training Agency], Nick Tate [chief executive of the School Curriculum and Assessment Authority] and Chris Woodhead [chief inspector]. The Downing Street Policy Unit is the problem. It has the habit of making education policy on the hoof. But even the Prime Minister is keen to talk to us,” he said.

The unions, however, are increasingly looking to Labour as the polls predict they could be the new political masters before the year is out. “It’s very interesting watching the unions, particularly the National Union of Teachers and the Association of Teachers and Lecturers jostling for position to be Labour’s favourite adviser,” said one rival association member.

The Labour party meanwhile seems keen to keep the unions at arm’s length and while general secretaries may be invited to dinners, they are not having a great deal of input into policy. Left-wing NUT members are also concerned that the democratisation proposed by general secretary Doug McAvoy is an attempt to fashion a “New NUT” in the image of Tony Blair’s party.

Christine Blower, who will become the NUT’s vice-president next month, said: “I am concerned that the NUT should remain a free and independent union and not be so concerned about rocking the boat for the Labour party.”

Michael Barber, dean of new initiatives at London University’s Institute of Education, believes the teacher unions may be able, if they stick together, to stop or sabotage Government policy, but they are less likely to be able to unite to move policy forward. Their relative strength and financial solvency paradoxically contributes to their weakness. Ministers (and employers) know they can play one union off against the other and if the teachers cannot agree on policy then any argument is diluted.

Last year the union conferences were buzzing with indignation over class size and motions demanding a strong response were passed. Yet action has been limited. The unions accept they have made little progress on class size but argue that forging alliances with parents and governors has made it a potent issue in what could be an election year.

They do claim some success in stemming redundancies. While not many teaching posts have been saved, negotiation with local authorities has greatly decreased the number of unwanted compulsory redundancies. The ATL calculates in nine out of ten cases unions have negotiated a deal, for example early retirement or retirement for ill-health. The future looks more difficult; the increase in part-time posts and temporary contracts makes it harder for unions to safeguard jobs.

The lowest point in recent history for the teacher unions was following the pay disputes of the 1980s. They were divided and battle-bruised. Their weakness enabled Kenneth Baker, the then Education Secretary, to push through radical legislation which has transformed the education system and lives of the profession.

There was one beneficiary: the Association of Teachers and Lecturers. The ATL has doubled in size in the past 10 years, recruiting many defectors during the dispute years. Peter Smith, the general secretary since 1988, has worked hard to bring the archaic Association of Masters and Mistresses Association into the 1990s and the name change was very much part of that.

There is little cachet to being known as the third largest teaching union, but recent attempts to liven up conference motions (AMMA was notorious for the abstainers winning a variety of votes) and rescheduling the conference is heightening the union’s profile.

“When we get press coverage it tends to be good, but often the media prefer something more dramatic to the ATL’s moderate and thoughtful responses, ” said a spokesman.

For Nigel de Gruchy, general secretary of the NASUWT, is King of the Quote. Always on hand to offer the media a pithy remark, his is increasingly becoming the most familiar face (and voice) of the teaching profession - although some would argue that a number of his shots from the hip, for example saying he would prefer troublemakers to truant rather than disrupt his members’ lessons, are not particularly helpful.

Even so it will be, inevitably, the NUT which will grab the headlines this Easter. The internal reforms that its general secretary, Doug McAvoy, is seeking mean war with the activists. And as Easter is traditionally a quiet time for the media, sensation-seeking newspapers and TV companies will have their fingers crossed for bad behaviour, particularly when Mrs Shephard is speaking.