The salary of the highest paid academy chain leader has soared to £370,000 – more than two-and-a-half times that of Prime Minister David Cameron.

Sir Daniel Moynihan, chief executive of the Harris Federation, saw his pay for running 28 schools increase by nearly £40,000 in 2014 – making him the highest paid boss of a multi-academy trust (MAT).

A joint investigation by Schools Week and Watchsted into the CEO pay and Ofsted performance of the 10 largest academy trusts, as defined by number of schools managed, has revealed that Sir Daniel’s salary level is £150,000 higher than that of the next-best paid academy boss, AET’s Ian Comfort.

Mr Comfort is chief executive of Academies Enterprise Trust (AET) – the largest chain in England. He received £220,000 in 2014 for running more than twice as many academies as the Harris Federation.

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Unison’s head of education, Jon Richards, whose union represents more than 250,000 support staff in UK state schools, told Schools Week: “The explosion in senior pay across many academy trusts over the past few years is completely disproportionate.

“In the same period, school support staff have endured year upon year of pay freezes and real-term pay cuts.”

Every Ofsted inspection carried out at academies since they joined the Harris Federation has resulted in a good or outstanding rating. Moynihan’s pay divided by the current number of good or outstanding ratings would therefore put the CEO’s cost at £19,474 per school.

According to Harris’s financial statements for the year to August 2014, many of the academies which received “excellent” Ofsted inspection results had been “very challenging schools previously in special measures”.

AET operates 67 academies nationally. Thirty-two of its 60 Ofsted inspections have been good or outstanding, putting Comfort’s cost for every such school at £6,875. But in October last year the Education Funding Agency issued AET with a financial notice to improve and 28 of its schools have received requires improvement or inadequate ratings while under its watch.

An AET spokesman told Schools Week: “Our objective is for every one of our academies to become outstanding as soon as possible, and we are making real progress in this direction.”

School business director Micon Metcalfe, who also trains other education leaders, said that academy trusts are free to set salaries for CEOs and senior leaders at any level “they think appropriate”. But she noted that trusts must bear in mind that “remuneration needs to be proportionate and … not be seen by the general public as contentious or inappropriate.”

Ms Metcalfe added: “I do think academy boards should take into account the overall performance of the chain when setting the CEO salary and have appropriate key performance indicators in place.”

Russell Hobby, general secretary of the National Association of Headteachers, also defended the high salaries.

He said: “It can be right to pay school leaders significant sums of money, particularly if they are leading many schools in challenging circumstances.

“This can represent good value in terms of raising standards for children. The crucial thing is that these decisions are made fairly, transparently and with due process to reassure the public that these decisions are right.”

Plymouth CAST paid its chief executive the lowest salary among the trusts investigated, with John Mannix receiving £53,333. The group’s 35 schools converted from the diocesan network to being part of a multi-academy trust in April last year. Only one of its schools has been inspected by Ofsted since the change took place.

Oasis Community Learning’s chief executive John Murphy was paid £150,000 in 2014. The academy group also paid 77 staff members more than £60,000 in 2014 compared to 44 in 2013.

A spokesperson said: “During the tenure of our current CEO – which commenced in September 2014 – Ofsted inspections have led to 58 per cent of academies being raised to good or better and 20 per cent being lifted out of a category of concern.”

A spokesperson for REAch2 said £135,000 was paid to deputy chief executive Cathie Paine. He said that the chief executive Steve Lancashire is paid £190,000 and is remunerated through the founding academy of REAch2 Hillyfield, where he is executive principal. He added: “REAch2 prides itself on providing excellent value for money to all of our academies.”