Former academies minister Lord Nash has been accused of “threatening to allow” an academy trust to “become financially unviable” unless it appointed his former business associate as chair.

Steve Munby, former chief executive of CfBT Schools Trust, which sponsors CST Academy Trust, has revealed the tale in his new book, accusing Nash of “abusing his position”.

In my opinion, this was an example of a minister abusing his position and going further than he had a right to do

In the book, entitled Imperfect Leadership, Munby talks about his time heading up the sponsor of CST, while it was under government scrutiny of its school performance and finances.

Munby said how CST, where he was also chair, was warned that a poorly performing but financially strong school would be rebrokered unless it improved, leaving the trust “bankrupt”.

In June 2015, Nash sent a “rather threatening” letter setting out how to avoid the rebrokerage.

It included 13 conditions, one of which was to make Nash’s former business colleague David Whittaker – a former investment director at Nash’s private equity firm Sovereign Capital – chair of CST.

Another condition was to appoint Whittaker and another Nash-approved candidate as members of the trust – meaning the original sponsor would be a minority member.

“I was deeply shocked. The minister was threatening to allow CST to become financially unviable unless David Whittaker was put in as chair of the board and unless CfBT were no longer the main sponsor,” Munby wrote.

“In my opinion, this was an example of a minister abusing his position and going further than he had a right to do.”

The CfBT board refused to insert Whittaker as chair of CST, and the school remained with the trust.

However, Nash did insist that Munby stand down as chair of CST. Munby highlighted that Nash was chair of the Future Academies trust and its sponsor, Future, at the time.

But Munby said he now felt Nash was “right to encourage me to stand down”.

The former academies minister told Schools Week he was “delighted” to hear that. He added Whittaker volunteered for the role “out of the kindness of his heart to help the academy movement pro bono and I have no doubt that he could have been of considerable assistance to CST”.

Whittaker said he was was offered a position on the board but they were clear they did not want him to be the chair.

“I declined, as I was only prepared to get involved if appointed chairman,” he said.

A DfE spokesperson said they took “decisive action, persuading the trust to make significant changes to address the governance weaknesses in the trust, and helping to bring about improvements. If a similar set of circumstances existed today the department would intervene in a similar way.”