Mr Justice Maurice Kay said the Education Secretary had done himself no credit when he incorrectly promised that children who already had a place in an all-through school would be allowed to continue. It was a "sorry state of affairs".
His comments came during an unsuccessful court challenge by a mother who found her daughter's assisted (state-funded) place had been axed when she applied to join the senior section of the school. Labour had promised in its pre-election manifesto to abolish the assisted places but to protect those children with them.
Rachel Begbie had asked the court to hold Mr Blunkett to his pre-election promises and fund her daughter's schooling. The test case is thought to affect up to 1,500 pupils currently in junior departments of private schools providing education up to the age of 18.