Doctors could be faced with angry patients questioning spending decisions if NHS reforms go ahead, the new leader of the Royal College of GPs has warned.
Clare Gerada criticised plans to put £80bn of annual funding into the hands of GPs as part of widespread reform.
Patients could end up begging doctors for life-saving drugs while drug companies lobby GPs, she warned.
The NHS has been told by Health Secretary Andrew Lansley to make up to £20bn of savings by 2014.
Mr Lansley believes GPs know what works best and wants to tap into their entrepreneurial spirit to drive improvement.
The plans move the responsibility of deciding who gets treatment from the National Institute for Health and Clinical Excellence and primary care trusts in England to GPs, from 2013.
"At worst, the negative impact for GPs could be patients lobbying outside their front door, saying 'You've got a nice BMW car but you will not allow me to have this cytotoxic drug that will give me three more months of life'," she told the Guardian newspaper.
"I'm concerned that my profession, GPs, will be exposed to lobbying by patients, patient groups and the pharma industry to fund or commission their bit of the service. There could be letters from MPs and patient groups, and begging letters from patients."
She added: "Patients might think that the decision made about their healthcare will be based on self-interest - GPs saving money for themselves rather than spending it on patients."
Currently about 80% of the budget is held by local managers working for the 151 primary care trusts in England.
Ministers want to transfer much of that responsibility to GPs working in consortiums across the country, phasing out primary care trusts and regional bodies known as strategic health authorities over the next few years.
But Dr Gerada predicted the demise of the NHS through such reform.
"I think it is the end of the NHS as we currently know it, which is a national, unified health service, with central policies and central planning, in the way that (Aneurin) Bevan imagined," she said.
A Department of Health spokeswoman said the reform was "a necessity", not an option.
"We share a common goal with the RCGP that we all want patients to get the best health and care services," she added.
Shadow health secretary John Healey said the plans were "signalling a break-up of the NHS that will see it move away from a consistency of service that can be accessed whatever people's means."
He accused Mr Lansley of not listening to warnings from doctors, nurses and health experts "to slow down on his high-cost, high-risk plans."