The closure of local A&E departments will put the lives of seriously ill patients at risk by making them travel further for treatment, a study claims.
The study said training of ambulance staff needs to improve
Researchers said it was time to debate the merits of big regional units after finding the risk of death went up with each mile travelled for urgent care.
The Emergency Medicine Journal research involved 10,000 cases in four ambulance services between 1997 and 2001.
But a government health tsar dismissed the study as outdated and irrelevant.
Researchers from the Medical Care Research Unit at the University of Sheffield insisted their study showed more research was needed into so-called "reconfiguration", in which local services are reduced in favour of specialist regional centres.
Many A&E departments have been, or are about to be, closed or turned into so-called minor injury units which deal with little more than "bumps and bruises", researchers said.
Meanwhile, health service bosses - with the backing of government - are overseeing the creation of "super" regional hospitals providing expert and complex care.
Just over 10,000 patients with problems including chest pain, respiratory conditions, injury, and haemorrhaging were examined in the study.
Some travelled up to 36 miles for treatment, but the average distance was around three miles.
In all, just over 6% - or 644 - of the patients died. However the risk of death rose by 1% for every six miles.
Those with breathing problems were most at risk compared to those with other conditions. Their chances of dying were 13% if the distance to hospital was between six and 12 miles, and 20% if this was 12 miles or more.
"Our data suggest that any changes that increase journey distance to hospital for all emergency patients may lead to an increase in mortality for a small number of patients with life-threatening medical emergencies, unless care is improved," the authors wrote.
But even if treatment in the ambulance were improved, a "trade-off" would have to be made, they claimed.
While it might be in the interests of heart and trauma patients to travel further for better care, it would be unacceptable for this to be done at the expense of patients with other conditions, they argued.
The government's director for primary care, Dr David Colin Thome, said the research did not take into account the changes made in ambulance care in recent years.
Studies suggest heart patients fare better at specialist units
In any event, only those with certain conditions would go to specialist centres, while other conditions - including many respiratory problems - would be treated locally, he said.
"Local casualty," he said, "will still be available."
But the Conservatives, who have launched a major campaign to stop the downgrading of district hospitals, said the study "undermines the government's claim that closures are determined on a clinical basis".
Shadow Health Secretary Andrew Lansley said: "The need to concentrate specialised services in some hospitals should not preclude access to local A&E services, but the government is using it as an excuse to close them down across the country."
Clinicians said some form of reconfiguration was a necessity, but that studies like this showed you could not have a "one size fits all" policy.
"The public has to realise there are risks and benefits to all aspects of medicine - and local is not always best," said Dermot O'Riordan of the Royal College of Surgeons.
"For some people the risk involved in travelling that extra distance is worth it in terms of the quality of care received at the other end. The mantra should be 'local where safe, centralised where necessary'."
Martin Shalley of the British Association for Emergency Medicine said: "There does need to be a change, a re-organisation, because there just aren't the specialists to go around.
"But it does have to be done very carefully to make sure that people don't have to travel vast distances."