Ambulance workers said today they were saddened but not surprised by their boss's decision to quit.

David Griffiths is resigning as chief executive of Sussex Ambulance Service and will leave next month.

He plans to develop a career working nationally and abroad with emergency medical services.

The Sussex service has been beset with problems in the last year and some staff believe this is partly the reason he is leaving.

There was industrial action over pay and working conditions.

Previous chairman Patrick Herbert was sacked after Government inspectors found a culture of bullying and harassment in the trust, although staff said he was made a scapegoat.

Former director of operations Trevor Anderson resigned last December after the Audit Commission found irregularities in ambulance response times. A follow-up report this year found the service had changed in the last 12 months and the system had improved. Relations between staff and managers had got better.

The service has struggled to meet the Government target of answering all emergency calls within eight minutes.

It recently got one star out of a possible three in the Government's ratings - which means it is underperforming in some areas.

A spokesman for the trust denied Mr Griffiths, 47, was leaving for any negative reason and said he was looking for a change of direction in his career.

Unions said the pressure to meet tough Government targets had not helped.

A spokesman for the Sussex ambulance branch of Unison said: "This is a sad but not unexpected loss when considering the pressures to achieve Government objectives and performance standards despite the service not being supported with sufficient investment to meet them.

"He is yet another member of the senior management team to leave the service in recent times and Unison is keen to ensure Government and local health authorities invest adequately to continue to improve patient care and staff welfare."

Mr Griffiths, 47, said: "Everyone associated with the service has worked tirelessly in the past few years to modernise the way we work.

"It is beginning to pay dividends, with real improvements in our operational performance standards and the quality of clinical care to our patients.

"We have recently received a very positive report from the Audit Commission and we have managed to sustain our one-star NHS rating, despite a difficult year.

"I have always been impressed by the commitment of everyone to improve the services they provide. It has been a pleasure and a privilege to lead the team."

Mr Griffiths was chief officer at East Sussex Ambulance Service from 1989 to 1995. He was appointed chief executive of Sussex Ambulance with the merger of East and West Sussex ambulance services.

The service is now beginning the hunt for a new chief executive.