Nick Clegg was accused of opportunism by his coalition colleagues as he defended his new plan to impose the national curriculum and qualified teachers on academies and free schools, insisting he was not creating a coalition crisis but parents.

Liberal Democrat policy had been that the freedom given to academies should be extended to all schools. Only last week, the Lib Dem schools minister, David Laws, told MPs that he supported unqualified teachers who were doing a superb job in classrooms.

Conservatives reacted with fury at Clegg's move, on which they had not been consulted, but the deputy prime minister described it as "a perfectly sincere difference of opinion". He said he would not be demanding that the Department for Education (DfE) tear up existing contracts with schools, implying his policy was for his party's manifesto rather than the remaining 18 months of government.

He said that he had aired his views privately within government, and that Laws's defence of unqualified teachers in the Commons on Thursday was an expression of support for government education policy.

Senior Tory sources said they were convinced Laws had been unaware of the details of Clegg's speech in advance and would not have been expecting his party leader to challenge a central tenet of coalition policy.

Speaking on Sky's Murnaghan programme, Clegg said he was "a great supporter of free schools and accountability" but added: "As we move to an era of greater autonomy, and schools have greater freedoms to decide things for themselves, we at the same time have to ask them to respect certain basic quality standards so that parents, regardless of where their son and daughter go to school, can be reassured that their children are going to be taught by qualified teachers [and] they are going to be taught the national curriculum like any other schools."

He said his party had endorsed his policy on qualified teachers at its spring conference this year.

But Laws, one of Clegg's closest allies, made no mention of a policy shift in his Commons statement. He specifically defended unqualified teachers, adding that the best way to monitor them was through the Ofsted inspection process.

Clegg's stance brings the Liberal Democrats closer to the Labour party position on the accountability of free schools and academies. It also makes it more difficult for him to sustain the attack on Labour's position on free schools as muddled.

Clegg said: "There are three positions here. The Labour party position would want to strangle school autonomy. They have always wanted to micro-manage schools. The Conservative party does want the minimum amount of basic standards and I in a sense support a sensible balance.

"Yes, give schools more autonomy and yet give reassurance regardless of whether the school is called a free school or an academy [that] children are taught by a qualified teacher to the same standard as any other school in the country."

He said the Liberal Democrat policy was not a state secret, arguing it had been openly adopted at the spring conference. "It is something I have made clear in public and privately for a long time," he said.

"Of course there are tensions and pinch points and it is not a crisis when some of these differences are articulated in private. It is a longstanding fact that we think differently."

The DfE insisted it would not backtrack on existing policy. A spokesperson said: "Free schools are raising standards and giving parents more choice. They are run by teachers – not local bureaucrats or Westminster politicians – and are free to set their own curriculum, decide how they spend their money and employ who they think are the best people for the job. This government is not going to take these freedoms away.

"Independent schools have always been able to hire brilliant people who have not got QTS [qualified teacher status]. Free schools and academies now have the same freedoms as independent schools to hire great linguists, computer scientists, engineers and other specialists so they can inspire their pupils."

The shadow education minister, Kevin Brennan, urged Clegg to use his powers to insist that only qualified teachers are permitted to teach in free school classrooms. He claimed Clegg "was acting like he is a tenant on Cameron's country estate rather than showing political leadership over free schools".

The shadow schools minister, Liz Truss, suggested the deputy prime minister had only made the announcement to placate activists in his own party, and questioned whether he really wanted to change the policy.