Instead he vowed to “put rocket boosters” under Tony Blair’s city academy programme.

But the Tory leader’s stance could lead to some of his shadow cabinet threatening to quit. Last week Shadow Education Secretary David Willetts caused uproar when he claimed grammar schools no longer helped bright pupils from poor areas.

Michael Howard, former Tory leader and ex-grammar schoolboy, and Lord Tebbit were furious. But Mr Cameron said not even Margaret Thatcher or John Major had created a grammar while prime minister.

“It’s delusional to talk about these things in the future when we didn’t do them in the past,” he said. He will focus on improving more than 3,000 comprehensives instead.

One Tory MP warned: “This is not going to be forgotten.”