The Iron Lady, burnished in the glow of the gold plate display behind her, declared that Labour’s abolition of her flagship education policy was an “appalling mistake”. Opting out was central to the philosophy of her government - freedom of choice.

Beside her on the top table were former education ministers John MacGregor and Angela Rumbold. The architect of the reform, Kenneth Baker, had sent his apologies, as had Kenneth Clarke and John Patten faithful bearers of the GM baton as education secretaries. Gillian Shephard, education secretary before the 1997 general election, had not been invited.

The host for the pound;75-per-head dinner was Sir Robert Balchin, chairman of the Grant-Maintained Schools Centre. Many guests were in the GM vanguard, including John McIntosh, head of the London Oratory, whose involvement dated from the policy’s early days, and whose celebrity was ensured when Tony Blair sent his sons to his school.

Sir Robert had a political message: “I firmly believe the British state education system has been changed by the freedoms it has tasted, in ways that will not easily be reversed. Once people have tasted and used independence well, it is not easily forgotten.

“With hindsight, radical legislation should have taken all secondary schools out. I am enormously sad that, after our wonderful start, the project fell out of sight and was almost repudiated during the last three years of the last administration.” Mrs Shephard’s absence was explained.

It was the 1988 Education Reform Act that introduced grant-maintained schools. And the legislation soon caused tensions between Kenneth Baker, the education secretary, and his Prime Minister. Margaret Thatcher saw opted- out schools as a way back to greater selection. Mr Baker resisted this. The tensions between Downing Street’s view of GM and the education department’s persisted - even after Labour was elected.

The main motive was to free schools from council yokes, particularly those in the so-called loony Left authorities. The reality was more complex. At the beginning there was a huge cash incentive. GM schools were given revenue from the local authority (the part held back for central services) and also had much readier access to capital grants for buildings.

Subsequent TES surveys found GM schools saying they were better staffed and resourced since the change. Some schools did become GM on ideological grounds, but others opted out to avoid closure, and it was the Conservative-controlled councils of Kent, Essex and Lincolnshire that saw large numbers leaving the authority.

The system of parental ballots which determining whether or not a school became GM, created a bitterness which remains today. Choice in Education, headed by Andrew Turner, a Conservative Oxfordshire councillor and would-be MP, became the political wing of the GM movement.

In opposition, Local Schools Information, lead by Martin Rogers, funded by local authorities, was set up. The two became rapid response units, winging their way up the motorways to schools which were balloting to put forward the arguments.

Mr Rogers said: “I attended almost 1,000 meetings and overwhelmingly the motive for opting out was money. What has to be remembered is that this money was going to GM schools at the expense of their neighbours.”

After the initial flurry, the numbers turning dwindled. The then education secretary John Patten remained gung ho and declared at the 1993 Tory party conference in Blackpool, that he would eat his hat if the majority of secondary schools did not opt out.

But his evangelism was not shared by his successor Gillian Shephard, whose political roots were in local government and she saw the logical conclusion of GM policy as the abolition of local authorities. She wasn’t sure that she wanted to go that far.

When she inherited Mr Patten’s desk, she was bemused to find a numbered card on it each day. Her private secretary told her they were the number of schools that had become GM. It wasn’t a service she asked to be continued. She instead focused on getting specialist schools established - and making them an option for both LEA and GM schools.

With the election looming and the writing on the wall for the Tories, anti-GM lobbyists saw the end in sight. But the Labour party’s 1995 document Diversity and Choice, filled them with dismay. While GM status was to go, Labour created three categories of school, community, aided and foundation school. Foundation, like GM schools, would remain the employers of staff and would have control of admissions.

But the greatest blow was to come. The announcement in 1995 that Tony Blair was to send his son to the GM London Oratory, was seen as a betrayal by all those who had lobbied and worked to prevent schools from opting out.

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