East of England Ambulance Service refused trust status
The East of England Ambulance Service's application to become an NHS Foundation Trust has been deferred because of its failure to meet response times.
Health watchdog Monitor said the trust had not reached patients within its 19-minute target.
Monitor also said it did not have a robust plan in place to address the problem.
The trust is expected to reapply for foundation status within the next six to 12 months.
During the deferral period the trust will need to demonstrate they have implemented an action plan to address the issue of response times.
The ambulance service's new interim chief executive, who started work on Monday, said: "Getting services to patients right and improving our performance is my focus.
"In the few days I have been in post I have had many good ideas already from staff that gives me real belief that we can transform our service."
Maria Ball, who chairs the trust, said it would be focused on addressing the points Monitor had raised.
Foundation trust status would allow the ambulance service to step away from government control and decide how to improve services.
It would also be able to control its own budget and would be more accountable to local communities.
The ambulance service covers Bedfordshire, Cambridgeshire, Essex, Hertfordshire, Norfolk and Suffolk.