In an internal message to staff on Wednesday, Dr Marsh did not explain the reasons for his earlier than expected departure.

He was brought in as interim chief executive of the East of England Ambulance Service Trust (EEAST) almost a year ago for two years, in circumstances which upset some of the then board.

He will leave next year as soon as a replacement is found.

Dr Marsh had exposed the trust's failings in a report in June last year, which found the board and senior management team had 'developed a sense of helplessness'.

Six months later, Dr Marsh came in to turn the trust around and work with those board members and managers.

His appointment prompted the then chairman, Geoff Harris, to complain to the chief executive of the NHS Trust Development Authority.

In a letter in November, which was leaked to West Midlands MP Tom Watson this June, Dr Harris said the board's directors were 'dismayed and extremely disappointed' by Dr Marsh's appointment.

It was a rocky start to chief executive-board relations and Dr Harris resigned when Dr Marsh began.

The new chief executive was set to stay for at least two years, while still working two days a week as head of the West Midlands Ambulance Service (WMAS).

His job advert will be going out at some point early in 2015.

The EEAST said his departure was always going to happen next year and it is likely to take months to find a replacement.

They were forced into releasing a statement about recruiting a replacement on Tuesday night because of call from the BBC and EDP.

Those enquiries came from a tweet sent by Tom Watson stating he understood Dr Marsh was leaving.

The EDP understands Dr Marsh told some staff last week he would be going.

There has also been speculation of tension between Dr Marsh and board members fuelled by fears he was leading the trust closer to his other employer – West Midlands Ambulance Service.

Dr Marsh did use ideas from the Midlands in his bid to improve the EEEAST and some WMAS managers visited the trust to share their ideas.

Staff were also given West Midlands ambulances to test, but decided not to use them.

The EEAST is currently looking at a West Midlands policy which allows staff to opt out of working alone.

'Our connection with West Midlands has been very positive,' Unison branch secretary Fraer Stevenson said.

In the last year, Dr Marsh has also had to deal with constrained budgets and endured negative headlines in the national press over his £232,000 a year pay packet and taxi costs to ferry him between his two jobs.

But the feeling among some of the region's MPs and unions is that he has been worth the money.

'He has rebuilt the service from the bottom up,' Suffolk Coastal MP Therese Coffey said. 'I'm a big fan of what he has achieved.'

Do you have a health story? Email tom.bristow@archant.co.uk.