The heads of leading independents have accused politicians of "cowardice" for not debating the issue of academic selection at schools in the general election campaign.
Bernard Trafford, former chairman of the Headmasters' and Headmistresses' Conference (HMC), which represents 250 elite fee-paying schools, said the issue was too embarrassing for politicians to talk about.
"It's ostrich-like - they won't discuss it," he said. "I think it's cowardice that they won't engage with this issue because they are so scared about raising it. They are in denial."
Mr Trafford, head of the #163;9,000-a-year Royal Grammar School in Newcastle and vice-chair at the HMC, said grammar schools out-performed other state schools.
"I don't see selection as a social ill," he said. "It allows children of similar ability to fly together. It's crazy that no politician wants to engage with it."
His comments come in the week that a report by educational charity the Sutton Trust said the 164 most socially selective comprehensives took on less pupils from income-deprived areas than the 164 grammars.
The report added that 97.7 per cent of the pupils in those grammars reached five GCSEs, including English and maths, compared with 66.7 per cent in the comprehensives, and that 92 of the 100 most socially selective establishments were state schools.
Mr Trafford's successor as HMC chairman, Andrew Grant, said selection works - but political parties were afraid of admitting so.
Mr Grant, head of the #163;12,690-a-year St Albans School, told The TES: "It's tacitly acknowledged that selection works. You can't have it without a larger proportion not being selected. It's the elephant in the room."
He accused politicians of double standards on the issue, pointing out that leading universities all had selection processes with entrance exams: "No government has difficulty with selection for universities, but we're seen as an embarrassment."
A spokesman for the Conservatives declined to comment, referring The TES to its policy on selective schools - which says it will not open any more grammars.
But Margaret Tulloch, of anti-selection pressure group Comprehensive Future, said: "Selection divides children up unfairly at an early age. It would be good to get Labour and the Tories to say they will end it."