Heart attack and stroke patients are still waiting longer than they should for an ambulance, and paramedics are leaving the service due to poor morale.
The East of England Ambulance Service NHS Trust failed to reach its target time for attending people in critical situations, where minutes can make the difference between life and death, and has blamed a lack of frontline staff.
A report by the trust showed that ambulances in Hertfordshire and Bedfordshire failed to reach 36 per cent of the most serious "immediately life threatening" callouts within their eight minute target time in June, 2.2 per cent worse than in May.
Callouts in this category include people who are unconscious, in cardiac arrest or suffering from a heart attack or stroke.
The number of ambulances reaching people classed as "serious but not life-threatening", such as fits or diabetic episodes, also worsened in June, with ambulances failing to reach 41 per cent of people within eight minutes, compared to 34 per cent in May.
The trust said it was tackling the problem by recruiting 400 student paramedics this year. However, one paramedic, who asked to not to be named, told the Watford Observer that existing staff were leaving the trust.
The paramedic said: "As much as the service says they are recruiting, a substantial number of staff are still leaving due to moral being so low.
"There are staff shortages in the Watford area and management are trying to paper over the cracks by offering extra shifts on overtime.
"Many people feel that they are too drained physically to do overtime as their normal shifts are so busy due to the shortfall."
The situation for emergency patients improved at the beginning of July, however, since the start of the financial year, the trust has only reached 68 per cent within eight minutes, seven per cent below its target.
The trust was also below its target for serious, but not life-threatening patients, having reached only 64 per cent within eight minutes.
Dr Anthony Marsh, chief executive of the East of England Ambulance Service NHS Trust said: "I joined the trust in January and identified and set out six key priorities to turnaround the trust, with the main focus on reducing long ambulance waits some of our patients have had to endure.
"We are tackling that by putting more staff on the front line and increasing ambulance cover. The first group of which are already working from ambulance stations across the region, as well as up-skilling our existing emergency medical technicians and emergency care assistants."
The trust said it has also introduced 34 new ambulances and 31 rapid response vehicles and claims that since January, the wait for a response to a life-threatening emergency has dropped by two minutes across Hertfordshire and Bedfordshire.
Additionally, the East of England Ambulance Service NHS Trust says that 24 staff are going through "extra training" across the two counties.
A dozen emergency care assistants are being trained as emergency medical technicians, 12 of which are being trained as paramedics.
In November last year, the Watford Observer reported that the trust needed an extra 421 employees and 50 new ambulances over the next four years to try and turn around their poor response times.
Dr Marsh added: "Additional ambulances are also on the road, and we launched a replacement programme to ensure no ambulance in our fleet is older than five years by next Spring.
"These actions are starting to make a difference and as more staff are recruited and trained, delays will reduce further and performance will improve."