A row over a decision to remove the chair of Ofsted from her post intensified today after a former top civil servant warned Michael Gove not to surround himself with "yes men".
As the Education Secretary prepared to make a major speech vowing to break down the "Berlin Wall" between state and private schools, Sir David Bell warned that the minister should "not believe his own hype" and allow daily political life to cut him off from outside ideas and thinking.
Sir David - who previously served alongside Mr Gove as the senior civil servant at the Department for Education - made the comments the day after Mr Gove faced accusations by his Lib Dem colleagues of trying to "politicise" the schools inspectorate.
It was revealed at the weekend that Mr Gove has decided not to reappoint Labour peer Baroness Morgan of Huyton for a second three-year term as Ofsted chair.
He paid a glowing tribute to Lady Morgan for her ''enormous contribution'' to the work of Ofsted, insisting that the move was to "refresh" the watchdog's leadership and denying claims that it was politically motivated.
But the decision was seized on by the Lib Dems as a fresh attempt to assert his influence over the regulator, with Mr Gove's normally loyal Lib Dem deputy David Laws accusing him of trying to pack the watchdog with his ''own people''.
Writing for the academic website The Conversation, Sir David, a who is now vice-chancellor of Reading University, warned Mr Gove that he risks becoming isolated by listening only to his own supporters.
He said: "The day-to-day grind of policy battles, firefighting and political ding-dong can start to cut you off from outside ideas and thinking.
"The row over Ofsted's leadership shows the importance of retaining and being seen to retain independent voices near the top - not simply 'yes men'."
Sir David went to suggest that there was a wide group of voices in the education sector that offer an "intelligent critique of where we are now".
"These people have been broadly supportive of successive governments' education reforms and, as a result, are not so easily dismissed," he said.
"They believe in improving our education system but they also advocate sensible debate. They should be listened to by politicians of all parties."
Sir David also had strong words for the main teaching unions, saying that their leaderships had "played right into the Government's hands over the past four years.
"Their barrage of industrial action and knee-jerk opposition to any change, has allowed the Education Secretary and his supporters to characterise them as cartoon-like bogeymen," he wrote.
"The unions' political naivety has been astonishing."
The row over Lady Morgan's departure comes just a week after Chief Inspector of Education Sir Michael Wilshaw voiced his anger at the Education Secretary in the wake of media reports that two right-wing thinks were drawing up plans to reform or even replace Ofsted.
Mr Gove was forced to issue a statement voicing his full support for Sir Michael and promising to dismiss any aides if they were found to be part of any ''dirty tricks'' campaign.
In a keynote speech today, Mr Gove is expected to call for the opportunities available in fee-paying schools to be opened up more pupils than ever before.
He will say it is his ambition is to raise standards in the state schools in England to the point where they are indistinguishable from their fee-paying counterparts.
Addressing the London Academy of Excellence, he will say the evidence shows "beyond any reasonable doubt" that English state education is starting to show a "sustained and significant improvement".
By further tapping into the expertise of the independent sector - which has already resulted in many independent schools sponsoring or co-sponsoring state academies - he will say that England's state schools can become the best in the world.
"Instead of reinforcing the Berlin Wall between state and private, as the current Labour leadership appear to want, we should break it down," he is expected to say. "Thanks to our reforms, private schools are opening their doors and their opportunities to more children than ever before."
Mr Gove, who signalled at the weekend that ultimately he wanted to move to a longer school day to enable state pupils to enjoy the extra curricula activities available in the fee-paying sector, will say he is determined to build on those achievements.
"I want to see state schools in England the best in the world," he will say.
"State schools where the vast majority of pupils have the grades and the skills to apply to university, if they want to; where a state pupil being accepted to Oxbridge is not a cause for celebration, but a matter of course; where it is the norm for state pupils to enjoy brilliant extra-curricular activities like sports, orchestras, cadets, choir, drama, debating, the Duke of Edinburgh scheme, and more.
"All those things are par for the course in the private sector - why shouldn't children in the state sector enjoy them? We know England's private schools are the best independent schools in the world. Why shouldn't our state schools be the best state schools in the world?