Tony Blair's flagship education reforms have been criticised by former Labour leader Neil Kinnock.
Neil Kinnock became a life peer in 2004
In a rare attack on Labour policy, Lord Kinnock said the reforms were "at best a distraction and at worst dangerous".
He said the white paper - which faces rebellion from Labour backbenchers and was criticised by deputy prime minister John Prescott - must change radically.
Mr Blair says the reforms, giving schools more independence and control over admissions, will boost standards.
But Lord Kinnock told The Guardian newspaper the white paper was "a strange document for something setting out such a crucial new strategic direction for education".
"It looks as if it is written by committee, and the committee should have spent more than an extra week on it," he said.
"Fragmentation will have a damaging effect on schools, individuals and ultimately the level of educational performance," he warned, saying that he did not believe the government's arguments about increased choice.
The ex-European Commissioner said he believes the changes proposed in the white paper will reduce parental involvement and lead to a "further fragmentation" of the English education system.
Lord Kinnock will next week launch a pamphlet attacking the reforms.
The pamphlet is written by Melissa Benn and Fiona Millar, the partner of former No 10 communications director Alastair Campbell.
Lord Kinnock told the paper he admired the campaign being waged by Ms Millar. Former education secretary Estelle Morris, now Lady Morris, will also attend the launch.
Lord Kinnock's attack steps up pressure on Education Secretary Ruth Kelly, who is facing questions about her future over revelations some registered sex offenders have been working in schools.
Last month Mr Prescott told the Sunday Telegraph he feared pupils from poorer backgrounds could lose out under a two-tier, class-ridden system.
Mr Prescott, who failed his 11-plus but earned a degree, said he was not "totally convinced major reform is necessary".
The prime minister also faces backbench rebellion with 100 Labour MPs threatening to vote down the reforms.
The prime minister says the reforms, which would allow schools to become independent trusts, will give them more say over admissions, staffing and finances
Education Secretary Ruth Kelly has said the changes will give schools the extra flexibility to offer better services, but will not mean a return to selection by ability.
Meanwhile, a survey of 805 school heads and assistant heads for The Guardian newspaper suggested 61% did not think successful schools should be able to expand.
Just 29% of heads agree with proposals for schools to be freed from direct local authority control.