UKIP leader Nigel Farage has said the Tories are out of touch on grammar schools and he hopes disgruntled Tory MPs will defect to his party.
The Tories say they would push the government's academies further
He said Tory leader David Cameron's advisers were largely ex-public schoolboys, and many backbenchers were "very tired of the Cameron project".
A decision to end traditional support for grammars has angered many Tory MPs.
But education spokesman David Willetts defended the policy, and said it was not an attack on existing grammars.
Earlier in the week the Tories announced they would end their traditional support for such schools and instead take Tony Blair's city academies project even further.
But it has been denounced as "ridiculous" and "absurd" by some angry Tory backbenchers.
On Sunday, Mr Farage said only his party could offer a choice on the issue.
"It's UKIP that believes in academic selection and believes in grammar schools - we know they work," he told BBC One's AM programme.
"The electorate will say: 'What's the difference between the Conservative Party and the Labour Party?' The answer is, not very much."
He accused Mr Cameron's "set" of being largely former Eton public schoolboys, suggesting they were out of touch with the "real world".
"I think this is a disconnect between the David Cameron set and real people," he said.
Asked whether the policy would cause Tory MPs to defect he said there were an "awful lot" of MPs who were tired of David Cameron's efforts to change the party.
He added: "Whether this proves to be the straw that breaks the camel's back, I don't know. I do think we are not very far away from that point."
Earlier in the week Mr Willetts said it was a "fantasy" to say selection at the age of 11 could be fair.
And he said a "shockingly low" number of children from poor backgrounds were getting into grammar schools, while middle class children were being coached to pass the exam.
But on Sunday he told the AM programme the Conservatives were not attacking existing grammar schools.
He said the party wanted to improve social mobility in the "large parts of the country where grammar schools have gone".
And he said a return to grammar schools would not be feasible or would not tackle the "big problem of declining opportunities in Britain today".
He added: "I am confident that that is going to improve social mobility in this country today which I think is a fundamental Conservative principle and I'm thinking afresh about how we can deliver that in education."
Former Conservative leader Michael Howard, who has been reported to be furious at Mr Willetts over his speech, has said he is making no comment on the row.