Changes to how the public has its say on the running of the NHS are set to fail because of a lack of funding, leading doctors have said.
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The British Medical Association said the structure of Local Involvement Networks (Links) was flawed and open to unacceptable variations.
The Conservatives have also criticised the groups, which will replace the existing patient forums in England.
But the government said Links groups were more suited to the modern NHS.
Links groups will differ from patient forums by covering a geographical area, rather than being connected to a specific NHS body.
They will also cover both health and social care, be able to inspect NHS premises and work more closely with the voluntary sector.
The BMA views are outlined in its response to a Health Select Committee inquiry on public and patient involvement in the NHS.
It said the proposals for Links, currently going through parliament, would mean fewer groups to represent patients.
And it warned the suggested £100,000 and £150,000 funding for each group will not be enough to pay for staff salaries, premises and running expenses.
Plans to allow Links groups to be run locally could also mean variations in quality and the possibility that they could be dominated by special interest groups, the BMA said.
Juliet Dunmur, deputy chairwoman of the BMA Patient Liaison Group, said: "Many people would like a say in how their health services are run, but have never been given the opportunity.
"If Links are to have any real influence they will need much more support than their predecessors ever received."
Sharon Grant, chair of the Commission for Patient and Public Involvement in Health (CPPIH) which oversaw the work of the patient forums, and which will close when Links groups take over, said the forums - and the CPPIH were set up on the back of poor legislation and progress had been difficult.
But she warned the creation of new networks would take too much time.
"At the very least this is all very bad timing, especially given the high priority which is said to be attached to creating a ?patient led NHS?.
And Katherine Murphy, of the Patients Association, said there had been too much change in how patients' views were represented in the NHS, with the closure of Community Health Councils and now patient forums.
"Why can't we just stand still and give these bodies time to make a difference?"
But a Department of Health spokeswoman said: "The current arrangements to support a stronger patient voice were designed to fit the health service five years ago.
"Since then, the NHS and social care system has changed and it is now time to strengthen peoples' voices further."
Shadow Health Minister John Baron criticised the way the plans for Links were added to the Local Government Bill rather than being included in health legislation.
In a separate development, the NHS Confederation, which represents the managers of most NHS organisations published an Ipsos Mori survey showing only 9% of those questioned thought politicians should have a say in which treatments are funded by the NHS.
The poll of just under 1,000 people found 70% think doctors should have a say, while 33% want patient representatives should be involved and 23% that managers should have a say.
Dr Gill Morgan, chief executive of the NHS Confederation, said clinicians and managers were working hard to meet the needs of patients within a system with "finite resources".
"It is reassuring to see, therefore, that the public believes it is clinicians, patient representatives and managers who are best equipped to make these tough choices - not national or local politicians."
The Conservatives said the NHS did not need "day-to-day meddling" from politicians.
Liberal Democrat health spokesman Norman Lamb said: "Any independence from politicians must go hand in hand with genuine accountability to patients and the wider community.
A Department of Health spokesperson said: "NICE was established precisely to make difficult decisions on the basis of the evidence and free from political interference."