An aide to the schools minister has resigned after saying he could not support the government's education reforms.
Labour MP Martin Salter quit his job as parliamentary private secretary to Jacqui Smith last night, saying he could not promote the policies outlined in the schools white paper.
"I cannot in all honesty be part of a government operation to promote a policy about which I have such reservations," he said in a statement.
The move comes as a blow for the government, which is already facing backbench revolts over health reforms and is set for a battle over proposals to give schools more freedom.
Critics argue the plans would allow schools to bring back selection, although ministers have fiercely refuted this, insisting the existing code of practice on admissions would not change.
The government says that it is simply extending the freedom to innovate already given to specialist schools and academies across the education sector.
However, last night Mr Salter said he feared that giving more power to schools and parents would benefit the middle classes at the expense of those on lower incomes.
The MP for Reading West also questioned plans, announced by education secretary Ruth Kelly last month, to give local education authorities (LEAs) a more strategic and less hands-on role.
"I am worried that the proposals could lead to pupils from poorer areas being disadvantaged as popular schools expand, and wealthier and better informed parents are able to set up their own schools," Mr Salter said.
"I also believe that local education policy should remain democratically accountable, which is why I have problems with plans to downgrade elected LEAs."
Mr Salter, who entered parliament as part of Labour's landslide victory in 1997, said he wanted to be free to work with Labour back benchers to put forward "positive proposals" on education reform.