The chief executive of the East of England Ambulance Service has called a sharp increase in emergency calls “concerning”.

The region's ambulance service saw a 22 per cent increase in the number of red calls - the most serious cases - in April compared to the same month last year and chief executive Robert Morton said the increase in demand was masking the progress the service was making.

Red 999 calls include patients in cardiac arrest, suffering serious breathing problems, or life-threatening traumatic injuries and the ambulance service must be respond to at least 75 per cent of those calls is eight minutes, as per government targets.

He said: "The sheer scale of growth in demand is masking some of the progress we are actually making. When we look at progress over the last two years, more people are receiving a response within the target timeframe last year than was the case in the previous year.

"While response times performance is improving week-on-week, we would like to see further improvements and expect to see this happen in June.

"Everyone is working extremely hard to deliver improved services to patients - we thank the hundreds of potential patients who do recognise the pressure we're under and use alternative NHS services, but this is not enough and we are aware that our utilisation rates continue to be among the highest in the country.

"This has to change if we want the service to become an employer of choice and one where our staff want to stay."

The ambulance service is working to implement measures to improve working conditions for staff, including better meal breaks and finishing on time more often, but Mr Morton warned that "the increasing activity, demand for performance improvement, and lack of capacity makes this a very difficult balance to achieve".

In 2014/2015, the service began recruiting up to 800 new student paramedics who are gaining practice out on the road, but this year, most of these students must return to university and will not begin to qualify and be eligible to be fully registered until next March - with regular cohorts qualifying and registering up to the middle of 2018. "These 800 students are part of a long term solution, not a short term fix," said Mr Morton.

"Right now, we do not have the capacity to deliver the services we are expected to deliver and we cannot continue to rely on short-term investment and hiring private ambulance services forever.

"That is why we are working with our commissioners on a long-term plan for sustainable and ongoing investment to service the ongoing increases in demand but we need to be realistic about timelines, as paramedics are not trained in weeks or months."

The service has consequently begun a round of ambitious recruitment and career work for patient-facing roles, extending the student paramedic programme to allow for 200 more people to commence the two-and-a-half year training programme, as well as introducing new roles.

Another measure to help the most seriously life-threatened patients has been the introduction in early May of co-response schemes with fire services in Hertfordshire, Cambridgeshire and Essex. So far, two patients have been successfully resuscitated at the scene by fire crews, and other counties are due to come on board this summer. This builds on the support from existing volunteer community first responder schemes.

"All of the work we are focused on is about us becoming a more clinically-focused organisation, that's patient drive and responsive, and I want to thank the public and our supporters for recognising our drive towards this.

"I want to thank my colleagues for their hard work and commitment as, despite the level of responses we need to make, they are providing very high levels of care and excellent patient experience," added Mr Morton.