A seachange in the way region's ambulance service operates could see it halve the number of traditional ambulances it has, replacing many with response cars, it has emerged.

The East of England Ambulance Service is undergoing a major shift in the way it deals with 999 calls from the public.

Changes to ambulance response targets mean more people dialling 999 could get a call back from a clinician rather than a visit by paramedics.

And as part of this new way of working, the ambulance service is looking at reducing its intensive care ambulance fleet size from 276 to 138 vehicles and increasing its response car fleet from 145 to 232 vehicles. It could also increase its 'intermediate tier' vehicles from 21 to 105.

The figures, from a report which will go before the service's board at a meeting next week, are based on how the service thinks its operations will change in the coming years.

Its estimates that by using more triage – whereby emergency patients are sorted into categories of priority for treatment – it will be able to select the best response, which means it will be making fewer 'transports' of patients in ambulances and instead sending out response cars or signposting patients to other services and care.

The changes, which still need to be approved and which are still subject to change in terms of figures, could be put in place with half of the intensive care ambulances withdrawn towards the end of 2012.

The ambulance service trust is also looking at the future of its operational estate, which it aims to reduce by 15pc.

It has already selected 19 depots, or hubs, and will then go on to identify satellite ambulance stations, response posts and 'dynamic standby locations' later this financial year. There are already hubs in Beacon Park, Gorleston, at Longwater Industrial Estate in Costessey and at the Queen Elizabeth Hospital in King's Lynn, and it intends to implement another in Bury St Edmunds.

A spokesman for the East of England Ambulance Service said the proposed changes to the service's estates and fleet was to meet the changes in the way the ambulance would be operating in the coming years.

She said: 'The ambulance estate and fleet are only funded because it can demonstrate a purpose to support care and if that purpose becomes superfluous we would rather spend it on patients.

'We have to review frequently to make sure we are not just turning the handle and spending money where we always did when the needs have changed. Both fleet and estate march to the beat of the patients' drum.'

The reports will be discussed at the board meeting of the ambulance service at 11am on Wednesday, May 25, at the Node Conference Centre, Hitchin Road, Codicote, Hertfordshire.

How the ambulance service is changing the way it responds to 999 calls:

From April 1, the East of England Ambulance Service no longer had to meet a 95pc target of sending an ambulance to serious, but not immediately life-threatening cases within 19 minutes.

The government's decision to scrap the target means that people ringing 999 could receive a call back from a clinician to further assess the seriousness of the case in some of these calls.

Emergency 999 calls to the ambulance service are prioritised into categories to ensure life-threatening cases receive the quickest response.

They used to be called category A, B and C calls, but they are now being called red and green calls.

The 75pc target to respond to 'red' calls – immediately life-threatening – within eight minutes remains. The service has now identified four less severe 'green' call categories below this, which will be dealt with in different ways, including getting a call back from the clinical support desk, which is manned by staff with clinical knowledge and who are able to ask more detailed questions than normal call handlers.

One option they will have is to refer callers to more appropriate NHS services, such as a walk-in centre, pharmacy or a GP.

Patients could also receive a visit from a response car, to enable a paramedic to carry out further assessment of the severity of the case or treat a patient at home.

Unison has previously said that filtering out some calls prior to sending an ambulance could be a good thing, as it would free up ambulances to go to people who genuinely need them.

However, it warned that the methods the trust uses to assess calls need to be robust in ensure patients do not slip through the net.