Plans for trained paramedics to treat patients on the spot, rather than taking them by ambulance to hospital, have come under fire from union leaders.
Patricia Hewitt, the Secretary of State for Health, insisted the scheme, under which "emergency care practitioners" would deal with nine out of ten urgent calls, would not put patients at risk.
But Ray Carrick, the assistant general secretary of the Ambulance Service Union, told the BBC that staff had concerns about the scheme. He said: "For it to work well, the scheme is going to be utterly dependent on the information that is passed from the call to our control room.
"So when somebody dials 999, what they tell our control is what everything is going to be based on, and that is not always accurate."
Mr Carrick said the new paramedics were likely to be experienced existing staff. "When they are taken out to do a training programme three or four months long, they will have to be covered ... and there are only so many people we can draw on to fill those vacancies."
The government-backed review to be published this week will claim that one million patients are taken to accident and emergency departments unnecessarily, and propose giving paramedics new skills to extend their care for patients.
Under the proposals, the traditional two-person ambulance would be reserved for the most serious cases, with lower-level problems dealt with by paramedics.
But Ms Hewitt said the NHS would "err on the side of caution" to ensure patients were not at risk.
"There is a new role for the ambulance service that is developing and that is, if you like, to take the hospital to the home," she said.
"A lot of the calls ... especially at night and at weekends don't actually need the patient to go to hospital. With extra training ... [paramedics] can go straight out to the patient's home and see and treat the patient, but ... if there turns out to be something more serious the patient will be brought to hospital."
She told Sky News: "This is not a cut in the service - this is a real improvement and it is very much what patients are telling us they want: more care, closer to home. This is not about cost; this is about reshaping the ambulance service."
The Conservatives were broadly supportive. Andrew Lansley, the shadow Health Secretary, said: "If we had a more integrated emergency service, this would help ensure that the most appropriate person deals with each case."Reuse content