Both NHS and private ambulances carry out patient transfers
Patients are being put at risk by inadequate hospital transfer arrangements, anaesthetists say.
A combination of NHS and private ambulances are responsible for ferrying people around sites in the UK.
But the Association of Anaesthetists said the vehicles were poorly equipped and called for a national transfer service to be established.
The Tories said the situation was unacceptable, but the government said the system should be working well.
The association warned the problem was only going to get worse in the future if it was not resolved.
The re-organisation of hospital services in England to create centres of excellence will mean more patients are gong to be transferred for specialist care.
And the anaesthetists also highlighted the EU working time directive which is being phased in gradually across the NHS.
They said later this year junior doctors' hours will be reduced, leading to a smaller pool of staff to transfer patients.
This could lead to key hospital staff being taken off wards to transfer patients, putting even more patients at risk, they added.
The report also criticised the facilities available on some ambulances with insufficient power supplies for medical equipment identified as one of the key areas of concern.
Some doctors had also reported they had to wait several hours for transfer vehicles to arrive after they were called.
The report put forward a series of recommendations to improve the system.
The most radical was the creation of a centrally managed transfer system to replace the current arrangements which are run by individual NHS trusts.
Other recommendations include better training standards and a reduction in transfer for non-clinical reasons - patients can find themselves transferred because of a lack of beds.
Dr David Goldhill, the chairman of the working group which drew up the report, said it was an issue that needed to be taken more seriously.
"There is no doubt that the situation we have at the moment in most areas is entirely unsatisfactory. The patients are in a vulnerable position."
Shadow health minister Mike Penning said government action was needed.
"When patients are vulnerable it is simply unacceptable that they be put at risk."
A Department of Health spokesman said the system did not need changing.
"We welcome this report. Its recommendations are in line with what is already considered good practice."