With the general election less than seven weeks away at the most, Mrs Shephard turned up the political heat, claiming that envy and hatred would smash everything that the 1,200 schools in the opted-out sector stood for.
"If you value your freedom, your ethos, your independence, your ability to make your own decisions
. . . then beware Labour's plans," Mrs Shephard told the annual conference of the Grant-Maintained Schools' Centre. "I care too much for GM schools to allow them to be destroyed for want of being warned.''
Alarm bells were already ringing. David Blunkett, the shadow education secretary, has clearly failed to convince GM schools that there will be no retribution under a Labour government.
While relationships between the GM movement and national Labour leadership are good, the sector claims hostility towards it is still rife in local education authorities.
GM schools fear that under a Labour government they will be picked on and possibly closed when local authorities have to get rid of surplus places. They claim that with councils once again controlling a chunk of their budgets, they will be penalised. They also argue that a Labour government with a small majority would do deals on GM status with local authorities, while Labour government with a big majority would not necessarily be good news because it could spell big changes. A hung Parliament would be the worst of all worlds.
"I just want to be left alone to do what I am doing at the moment," said Margaret Lenton, head of Slough grammar school. "I want what I have got at the moment - my freedom."
"We have got to be able to keep the characteristics that identify us as GM - independence, a sense of ownership and control," said Alan Roach, head of Chalvedon School in Basildon. It was a message heard time and again over two days of the conference in Birmingham.
Opting out is still highly political. And at this general election there is a lot to play for - not least the votes of the 1.3 million parents who have children in GM schools.
It is an issue that divides the parties. The Liberal Democrats would return GM schools to local authority control. Under Labour, GM schools are likely to become foundation schools (with a similar governing body, but a stronger role for parents and two LEA governors), and they could have 10 per cent of their budgets returned to local authorities.
John Major has said he wants all state schools to become self-governing and the Government has been considering making all secondary schools hold an opt-out ballot if the Conservatives win the election.
GM heads and governors are not convinced by the argument that they are safe because Tony Blair, the Labour leader, has sent his son to the London Oratory, a GM school.
"Can a leopard really change its spots?" asked Pauline Latham, chairman of the Grant-Maintained Schools Advisory Committee.
Last month Labour met the committee of the Association of Heads of Grant-Maintained Schools and the Funding Agency for Schools, which administers opt-out finance.
"David Blunkett was very open, friendly, charming and plausible," said Mrs Latham. "But he doesn't understand the detail and neither do the people who work with him. He says there will be no retribution against GM schools but I don't know how he can control the people on the ground who are still hostile."
What worries the sector is Labour's proposal that councils should devolve a minimum 90 per cent of their schools budget. Although this is an increase on the present 85 per cent figure, it means that GM schools, which currently enjoy 100 per cent delegation, would lose 10 per cent of their funding. This could mean a cut of up to o300,000 in a large secondary, GM school leaders claim.
GM heads believe there will be a dramatic growth in the sector if the Conservatives retain power at the election, claiming 185 schools in Kent and East Anglia alone have already expressed an interest.
Brother Francis Patterson, head of St Francis Xavier College in Liverpool, said there would be a flood of interest from church schools and predicted the Conference of Bishops would change its "hands-off" stance. Under a Labour government, he said, the majority of denominational GM schools would choose to become foundation schools rather than return to voluntary-aided status.