The row between David Laws and Michael Gove in the education department over the future of the schools watchdog deepened, with the Liberal Democrat minister speaking out over the decision not to reappoint Ofsted's chairwoman.
Relations between the senior Lib Dem and his departmental boss the Education Secretary have been strained by Mr Gove's decision not to retain Labour peer Baroness Morgan as the head of Ofsted, raising the possibility of a Tory supporter taking the job.
In a fresh rift Mr Laws has now called for Ofsted to be given a new role investigating chains running academy schools, a move which has previously been resisted by the Department for Education (DfE).
Mr Laws criticised Mr Gove's decision not to retain Baroness Morgan, amid rumours that Tory donor Theodore Agnew was being lined up for the post.
" I don't think it is one of the best decisions that Michael Gove has ever made," Mr Laws told The Independent. "I personally think that Sally Morgan has done a fantastic job as chair of Ofsted. I would rather she had remained and had her term renewed."
The Independent reported that Mr Laws had made clear he intends to stop Mr Gove imposing Mr Agnew as Lady Morgan's successor.
But a DfE source said Mr Laws was "playing political games" and the final decision on Lady Morgan's replacement would rest with Mr Gove.
The Education Secretary has insisted the appointment would be made on merit and that it would be "quite wrong" to rule out a suitable candidate simply because he was a Conservative.
Mr Laws said: "Quality has to be the factor - the ability to do the job, which includes the ability to be independent from the Department for Education and ministers.
"We just cannot end up in a situation where posts of this type are selected on the basis of which political party you are in rather than your competence for the job."
Mr Laws also set out his desire to place academy chains under the same level of scrutiny as individual schools.
He said: "When the academies programme started, it had a lot of enemies and was regarded as a precious flower that needed protection. But this flower has now grown strong enough to survive in the full heat of the sun.
"There are some really good local authorities and there are still some terrible ones. In the same way, there are some good academy groups doing an absolutely fantastic job - like Ark and Harris - and some not doing so well."
The cross-party Education Select Committee recommended last year that Ofsted should be given the power to inspect chains, but the DfE has rejected the suggestion.
The Lib Dem minister said: "Ofsted must be able to shine a spotlight wherever it wants to. I don't want there are to be any constraints. It ought to be able to inspect the chains."
Mr Laws acknowledged that the measure could not be passed before the general election but it would be in the Lib Dems' 2015 manifesto, the newspaper reported.
The intervention by Mr Laws was dismissed by the Tory side of the DfE.
A source said: "As Michael Gove said on Monday, an independent panel will asses candidates for the next chair of Ofsted and he as Secretary of State will make the final decision.
"We've spent this week telling parents about our plans for tougher discipline, a longer school day and making state schools as good as private schools. If the Lib Dems want to carry on playing political games, that's up to them."
Kevin Brennan, Labour's shadow schools minister, said: "Nick Clegg and David Laws gave the go ahead to Michael Gove's unchecked expansion of some academy chains.
"As a result, school standards have suffered. This is a Lib Dem record as much as it is that of the Tories. The Lib Dems are now trying to play catch up with Labour."