A government review is taking place to ensure an action plan to improve the East of England Ambulance Service brings the trust up to the required standard.
A Department of Health spokesman said “serious performance issues” were being tackled by the trust itself, but that the review would “independently verify” that correct action was being taken.
Concerns have been raised in recent months over response times, and the review will be led by West Midlands Ambulance Service boss Anthony Marsh.
Health minister Lord Howe said: “There have been concerns about the performance of this ambulance service for some time.
“Whilst the management team have put measures in place to address these issues, I believe it is essential that a review now takes place to examine whether these actions are both adequate and soundly based.
“Having met with local MPs and ambulance staff in recent weeks, I am in no doubt that this is the right course of action to ensure that patients and the public in the East of England get the high standard of emergency service that they are entitled to expect.”