Triage at this stage could make a big difference

The research, published in the Journal of the Royal Society of Medicine, also suggests a different system would cut the number of road accidents involving ambulances.

In 2000-2001 there were 328 accidents involving ambulances in Scotland alone, the researchers discovered.

The research is based on a study of more than 500 patients taken to Ninewells' casualty unit following a 999 call.

The team aimed to look at the implications of applying triage criteria, assessing which cases are most urgent, to incoming emergency calls before ambulances are sent out.

They collected data to find out how many patients had genuinely needed the fastest possible response by assessing if they had any emergency conditions, like heart attack.

'Blue lights and sirens'

This was then compared with the information given by the person who made the 999 call, to see if triage criteria could have been applied.

Dr William Morrison, who led the research, said: "Many inappropriate calls are made by the public in good faith, and it would be unreasonable to expect the average 999 caller to decide how urgent a medical emergency is.

"Even under our suggested system, where the ambulance dispatcher makes simple prioritisation decisions, we emphasise that triage criteria must be safe enough to ensure patients who genuinely need a rapid response are not missed."

Heart attack symptoms would constitute an emergency

Dr Morrison said ambulance dispatchers could have cut the number sent out by at least 23%, simply by identifying patients who did not actually need hospital admission.

The researchers concluded that 55% of all calls for emergency ambulances did not merit an immediate response.

Research also showed that the number of ambulance callouts rose during the months the study was carried out, with no increase in resources to match.

Dr Morrison said: "The response to true emergency calls can be delayed if an ambulance is dealing with some minor incidents.

"An immediate response puts ambulance personnel and other road users at risk and may make no difference to the outcome of the patient."

The study, called 'Blue lights and sirens?' suggests that if response times to urgent cases could be cut from 14 to eight minutes, another 300,000 emergencies could be reached each year.

Earlier this year the Scottish Ambulance Service proposed a change to the system to prioritise the most urgent emergency calls.

The suggestion could be fully implemented within two years if it receives the go-ahead from the Scottish Executive.