The Charity Commission has taken action to remind the key organisation responsible for promoting free schools that it must remain independent, following a series of accusations that it is politically biased.
The watchdog has written to the New Schools Network about the need for it to be impartial in its role advising parents, academy sponsors and teachers who are considering setting up free schools.
A number of concerns have been raised about the charity, which is headed by Rachel Wolf, a 25-year-old former adviser to education secretary Michael Gove, after it was awarded a #163;500,000 grant from public funds.
Last month, it was revealed that the Department for Education failed to invite applications before handing the money to the charity.
A formal complaint was made to the Charity Commission by Labour backbencher Lisa Nandy, who raised questions about the New Schools Network's impartiality, given Ms Wolf's links to Mr Gove.
While the commission said it had been "reassured" that the charity had been acting appropriately, it was required to press home the importance of remaining independent.
David Bell, permanent secretary at the Department for Education, also wrote to shadow education secretary Andy Burnham this week stating that the appointment of the charity was above board. Mr Bell added that, under the previous Labour government, 84 grants were awarded to education bodies in a similar fashion without a tendering process.
A spokesperson for the Charity Commission said: "A complaint was submitted to the Charity Commission last month about the independence of the charity the New Schools Network... We were already aware of concerns raised in the media about this matter and had contacted the charity's trustees to request further information.
"We have reminded the trustees of their duties and responsibilities and provided them with regulatory advice on ensuring the charity's continued independence and on its activities. Our case is now closed."
Ms Nandy, a member of the Commons education select committee, said the commission's intervention highlighted a "lack of transparency" in awarding the grant to what she called an "untried organisation with links to the Conservative party, without any tendering process".
She added: "The commission makes clear that it is the Department for Education's responsibility to ensure there is no conflict of interest between the New Schools Network's advisory role and its other financial donors."
The Wigan MP also cited the network's refusal so far to reveal the nature of its donors, despite this being held as good practice by the Charity Commission.
But Ms Wolf said the complaints were politically motivated. "The Charity Commission was asked to look into us by activists who are ideologically opposed to free schools and who dislike what we do," she said.
"No one who understands charity law will be surprised to hear that the Charity Commission wrote to us making it clear we are operating in accordance with its rules."