Appointment follows rows within government over role and is first senior appointment by new education secretary

A teaching union has questioned appointment of a trustee of Britain's largest academy chain group as chairman of the schools regulator Ofsted, in what was a surprise announcement meant to calm some of the internal conflicts within the coalition.

David Hoare, former chairman of the mail company DX Group and a trustee of AET, the largest academy group in the UK, is the first senior appointment by Nicky Morgan, the new education secretary.

Critics have pointed out that AET has faced recent criticisms for the way it has run several schools.

Hoare is facing the embarrassing prospect of seeing his new body criticise his chain over the coming months. Ministers wrote to five schools in the AET chain about "unacceptable standards" last November. Ofsted's verdict was due to be published this week but was delayed. The report is now expected at the end of August or in early September.

His appointment on Thursday follows bitter rows within the government and the education sector over the role. Hoare's appointment will be less controversial than former frontrunner and Tory donor David Ross would have been.

But it has been viewed with suspicion by Kevin Courtney, deputy general secretary of the National Union of Teachers. "Teachers will view today's appointment as further evidence of the government's politicisation of school inspection," he said. "The new chair will need to demonstrate his competence to chair the school inspectorate in an impartial manner with regard to all academy and community schools," he added.

The post became vacant in February when the then education secretary Michael Gove failed to renew the contract of the then chair, Sally Morgan, who was a senior aide to Tony Blair when he was prime minister. She said there was a "determined effort" to appoint a Conservative to the job. The multimillionaire Carphone Warehouse co-founder Ross was expected to be chosen.

Tristram Hunt MP, Labour's shadow education secretary, said : "Playing politics with children's education by filling posts with the Tories' nearest and dearest is not acceptable." Gove's unexpected decision not to extend Morgan's three-year contract caused a damaging coalition row with the schools minister, David Laws. The Lib Dems suggested Gove had been trying to politicise the post, which the Tories denied. They insisted the selection process was overseen by an independent panel, and Downing Street said appointments were made on merit.

Hoare, who was schooled at the exclusive private school Marlborough College, has a 40-year business career, with a sideline in turning around failing companies. He started out in the oil industry, at Esso, before a 10-year stint at the Bain consultancy, and has been chairman of a number of companies including Virgin Express, Paragon Group and Laura Ashley. He is also a trustee of the Teenage Cancer Trust.

The DX Group was owned via a holding company based in the tax haven of the Cayman Islands until February, when the company was floated on the Stock Exchange. Its new holding company is domiciled in the UK for tax purposes. Accounts for the end of June 2011 say that Hoare is a director of the holding company and that it is registered in the UK for tax purposes. A spokesman for DX said that the company is based in the UK for tax purposes.

Last year AET, which runs 77 schools, was criticised by Gove for its performance in managing schools and was barred from managing any more along with several other academy chains.

Hoare was appointed in an unpaid capacity after the chain had gone through a period of rapid expansion in 2011-12. He will stand down from the role in September.

In a statement issued through the education department, Hoare said he planned to work closely with Sir Michael Wilshaw, chief inspector of schools, who urged Gove not to dismiss Morgan. "I am very happy to be taking up this appointment. I look forward to working closely with Sir Michael Wilshaw to raise quality in children's services and standards in our schools and colleges - especially for disadvantaged pupils," he said.

In the same statement, Morgan said his leadership skills would be crucial to helping Ofsted through a significant period of reform.

"I am confident that his strong track record in business and the passion he demonstrated throughout the interview process will be of huge benefit to Ofsted. He and Sir Michael Wilshaw will make a superb team," she said.

His appointment is an indication that relations between the Conservatives and Lib Dems in the Department for Education have improved. Gove was demoted to chief whip in David Cameron's reshuffle this month.

• This article was amended on the 6 August 2014. An earlier version stated that the DX group was owned via a holding company based in the tax haven of the Cayman Islands. This is no longer so.