The East of England Ambulance Service (EEAST) will look to recruit a new chief executive in January, but insist the man currently in the £232,000-a-year post is going nowhere until they find a replacement.
Anthony Marsh will step a side earlier than planned in the new year when a new chief executive is found.
Mr Marsh, who is also the chief executive of West Midlands Ambulance Service, was brought in on a two-year contract 11 months ago to turn the struggling service around.
He has scored some successes in recruiting new student paramedics and tackling response times, but will leave before his contract is up.
Mr Marsh, whose high salary was branded 'obscene' by Health Minister and Suffolk MP Dr Dan Poulter in August, has split his time between the two ambulance trusts.
The trust revealed last night that two previous efforts to recruit a chief executive had proved fruitless.
The service, which has been criticised in the last two years by patients, commissioners, MPs and the health regulator for slow response times, wants a long-term, permanent leader.
A spokesman said: 'Anthony Marsh, who is also chief executive of the West Midlands Ambulance Service Foundation Trust, was brought in to accelerate improvements in immediate service delivery and to build the foundations for long term sustainability for up to a two year period.
'As a result of a series of actions that he put in place when he took over in January long ambulance delays are significantly reduced, performance is improving, complaints are down, and compliments are up, although we recognise there is still much work for us to do.
'Following two previous unsuccessful attempts to recruit a chief executive, the board has always been clear that it will plan a new recruitment programme in 2015 and this remains the case. In the meantime, Anthony will continue as chief executive and continue to drive through service improvements.'
Denise Burke, from the Act on Ambulances campaign and Labour's prospective parliamentary candidate for North Norfolk, said: 'We still have very poor response times in North Norfolk even before the onset of winter, and we still haven't truly moved on from the issues that dogged the service two years ago.
'It's time Lord Howe (health minister for ambulances) left Westminster and visited us in North Norfolk so we can hear for ourselves what the government plans to do for residents here who desperately want to see improvements in response times.'
North Norfolk MP and care minister Norman Lamb said in August it was 'essential' that the EEAST kept Mr Marsh.
Fraer Stevenson, UNISON branch secretary at the trust, said: 'It's hard to see how we will attract someone with the experience or supportive attitude that Anthony Marsh has demonstrated and it's very disappointing that this decision has been made while we are in such a fragile state.
'To say we're in recovery is a small part of a very big picture, and while we've made good progress over recruitment, we are very far from out of the woods.
'Sickness is still high and the number one sickness issue is still stress and mental health. Cultural change is still desperately needed and this has been very difficult to address.
'I'm certain the news that Anthony Marsh is to leave the trust will impact on confidence and morale significantly.'
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