The NHS has announced an overhaul of ambulance response targets, which will mean fewer 999 calls being treated as requests about life-threatening events and therefore requiring the quickest response time.

In the biggest shake-up of the system in 40 years paramedics will also be expected to get to the most urgent cases more quickly. Officials said that the changes would allow ambulance crews more time to help the people most in need.

Half of all calls for ambulances are considered to be related to life-threatening cases, and NHS paramedics are expected to arrive within eight minutes.

But NHS England said that many calls did not, in fact, relate to such serious cases and therefore did not require the immediate arrival of paramedics. Under the new system, which will start in November, just 8% of call-outs will be classed as needing the quickest response.

The changes mean that the most serious calls, including cases where patients are not breathing, will now need an average response time of seven minutes, with a maximum of 15 minutes for 90% of patients.

However, other patients, such as those with a suspected heart attack or stroke – who used to require a similarly rapid response – will be moved to the “emergency” category and wait longer for help. The response will be within a maximum 40 minutes for 90% of patients, but typically within 18 minutes.

The overhaul comes amid concerns over the failure to meet ambulance response targets. Every ambulance service in England failed to meet targets in the last 16 months. The East of England ambulance trust was criticised for jeopardising patient safety by sending cars instead of fully equipped vehicles.

Under the new system call handlers will get more time to deal with less-urgent calls to make sure they send appropriate help. The time to assess a patient over the phone will increase from 60 seconds to four minutes.

Medical experts welcomed the move, which has been piloted on 14m 999 calls over the past year and a half. They said they hoped the new system would mean not immediately sending out a response car or other inappropriate vehicle in order to hit time targets.

Keith Willett, director for acute care for NHS England, said the system as it stood was not working because crews were dispatched unnecessarily to “stop the clock” and hit targets.

The professor added: “The ambulance service only has 60 seconds to make a decision about what is wrong with a patient and where they are. That frequently takes longer to achieve but after that time limit they must dispatch an ambulance.” He added that target chasing behaviour meant rapid response crews and motorbikes were sent out unnecessarily, creating an “inefficient and wasteful system”.

The old system, he said, had led to “hidden” waits as patients were expected to wait until an ambulance arrived, and though a responder might get to them in time, by bike or car, there would still be a delay in treatment.

At one of the pilot sites, it was reported that a cardiac arrest patient received a response 30 seconds quicker than they

Jonathan Ashworth, the shadow health secretary, criticised the government for failing to hit any of the NHS ambulance targets since May 2015, and welcomed a system that would be updated. “NHS ambulance trusts must now be given every support to build a new system which has the support of paramedics and patients alike.”

Taj Hassan, president of the Royal College of Emergency Medicine, said: “Response times will be more appropriate according to the patient’s need, and trials have suggested that ambulances could arrive up to three minutes quicker to the most serious incidents – time which can make the difference between life and death.”