Left-wing Labour MP Diane Abbott has been accused of hypocrisy for deciding to send her son to a private school.
MP Diane Abbott has been critical of colleagues' school choices
She is believed to have chosen to pay £10,000 a year for James, 12, to attend City of London School, rather than a comprehensive near her home in Hackney, north London.
Ms Abbott has previously been strongly critical of Labour colleagues Harriet Harman and Tony Blair for their school choices.
Eamonn O'Kane, general secretary of the NASUWT teaching union, said she was condoning "apartheid" between state and private education in London.
'Doesn't look good'
He told BBC News Online: "There have been problems with education in Hackney but it's beginning to be turned around.
"It's regrettable that middle-class parents appear to be keen to leave the state education system.
"Given Diane's previous comments, and her strong support of state education, this is not going to look very good."
Ms Abbott, MP for Hackney North and Stoke Newington since 1987, once criticised the then Solicitor General, Harriet Harman, for sending her son to a selective school in Orpington, Kent.
Ms Abbott said: "She made the Labour Party look as if we do one thing and say another."
She also criticised Tony Blair for sending his eldest son Euan to the London Oratory, a prestigious comprehensive outside the borough in which he was living at the time
City of London school came 43rd out of 287 independent schools in this year's A-level table.
Earlier this year, the government set up the Learning Trust, a not-for-profit company to run schools in Hackney.
This summer, the borough reported that 36.8% of pupils had gained five grades A* to C at GCSE. The national average is 51%.
Mr O'Kane said: "Private schools have far more resources that those run by the state.
"Diane's action in all this will show up her earlier words in sharp terms."
A spokesman for Ms Abbott said she was refusing to comment on the issue.