Concessions on Tony Blair's flagship school reforms will have to be more than cosmetic to win Labour critics round, former Education Secretary Estelle Morris has warned.
Baroness Morris, the ex-Birmingham Yardley MP, said MPs were not seeking to "score points" from the Government but expected negotiations to focus on the "substance" of the moves.
Her comments followed a stark warning by leading Blairite Stephen Byers that it was "untenable" for the Prime Minister to push the reforms through by relying on Tories to out- vote Labour rebels.
Baroness Morris, a prominent critic of the reforms, said if schools became more independent a framework was needed to ensure accountability to the wider community.
The proposals for independent trust schools set out in Education Secretary Ruth Kelly's White Paper have sparked concern among up to 100 Labour MPs, who fear that removing schools from Local Educational Authority control could create a two-tier system.
However, Deputy Prime Minister John Prescott dropped his opposition to the changes after reportedly being convinced by Mr Blair that the changes would not penalise poorer children.
Speculation has been mounting that Ministers are poised to make a series of concessions in a bid to avert a potentially-shattering Commons defeat.
Ms Kelly is expected to outline the Government's concessions at Labour's spring conference next weekend with a Bill anticipated in late February or early March.
Baroness Morris said: "I sense that the Government is saying 'OK, we do realise that this independence thing can go too far and we have acknowledged that schools are part of a wider system'.
"I have been in the Labour Party since I was 16. This is the very first time, both as an ordinary member, in opposition and in government that I've chosen to speak against my party and I don't do it lightly. The reason I do it is because the decisions we take now will really set in train school changes for the next decade."
Earlier, Mr Byers predicted that the majority of the parliamentary party would be satisfied by the expected concessions but he acknowledged that the Prime Minister knew his future was at risk if he failed to get his backbenchers on side.