Allyson Pollock, professor of public health research and policy at Queen Mary University of London, warned reforms in the NHS south of the Border could result in "serious" consequences for Scotland by translating into reduced funding through the Barnett formula.
Her warning seriously undermines claims by Better Together spokesmen, including its leader Alistair Darling at last week's final TV debate with First Minister Alex Salmond, that devolution protects the Scottish NHS from the creeping privatisation south of the Border.
She said a Yes vote would free Scotland from the "stranglehold" of the Westminster Treasury by allowing politicians to control public finances and NHS policy.
Her comments support Salmond's assertion that any cutbacks in England could hurt the health service in Scotland. In last week's debate he warned that, while the Scottish Government has operational control of the health service, it was a "serious problem" to be without financial control of it. Darling accused the First Minister of "scaremongering".
Pollock, who is a leading authority on the implications of privatisation for public services, said: "In the absence of any reversal of neoliberal policies in England, the clearest way to defend and promote the principle of a public NHS is to vote for Scotland to have full powers and responsibilities of an independent country."
Government critics have raised concerns the NHS in England is on a path towards an American-style healthcare system. Central to this has been the Health and Social Care Act of 2012, dubbed one of the most radical plans in the history of the health service, which included encouraging greater involvement by the private sector.
Pollock told the Sunday Herald: "Although people find this extraordinary and can't believe it, the Health and Social Care Act of 2012 has abolished the NHS in England as a universal service. The NHS is reduced to a funding stream and a logo; increasingly all the services are going to be contracted in the marketplace.
"It abolished the duty on the Secretary of State for Health to secure and provide comprehensive healthcare; that is a duty that still holds in Scotland, but doesn't hold in England. If the basis for a national health service has changed so markedly in England - if there is no duty to secure and provide universal healthcare - then what will happen is (public) funding can be withdrawn, and private funding will take its place. If you are closing services and reducing them, people only have two choices - to go without care or pay privately."
Pollock criticised politicians in Scotland for not taking more of a stance in opposing the act when it was going through Westminster. She added: "Scotland is very vulnerable because of what is happening in England - and any reductions in funding for England will translate through the Barnett formula to Scotland."
The Scottish Government has stated that in the event of independence, NHS services will not change the way health services are delivered. Funding for health care in 2014-15 is £12 billion, which the Scottish Government says includes an increase in funding of around £285m as a result of Barnett consequentials arising from increased spending on health in England.
At the heart of the debate over the NHS is how this will look in the future - and the potential for increasing privatisation in England is not the only concern.
Dr Willie Wilson, chair of the pro-independence group NHS for Yes, which has around 300 members, said another issue was the £25 billion of cuts which Chancellor George Osborne has said will have to be made after the election next year to "balance the books".
"If we vote No, then we are faced with what Osborne has promised of £25bn additional cuts," he said.
"There is no way Scotland's voters can wait until the Westminster elections and think they can avoid getting these cuts."
Wilson also queried whether the Barnett formula would remain in place in the event of a No vote. Last December, David Cameron said a change to the formula was "not on the horizon", but in June, accountancy expert Professor David Heald of Aberdeen University told a committee of MSPs that debate over the amount of spending Scotland received would be likely to re-emerge if there were a No vote. Wilson added: "If Ukip and the Tories are forming the next government after 2015, I'll bet the Barnett formula will be swept aside."
Health unions in Scotland, which are remaining neutral in the referendum, were reluctant to directly comment. A spokeswoman for the British Medical Association, said: "The BMA has opposed reforms in England. The model of the NHS in Scotland is the closest to that of the BMA's own policy and we absolutely support the principles of an NHS that is publicly provided and publicly delivered."
However, a spokesman for Better Together said remaining part of the UK would ensure the "best of both worlds for our NHS". He said: "We benefit from the strength of the wider UK economy to pay for our NHS. If we leave the UK then the experts at the impartial Institute for Fiscal Studies say we would need tax rises or spending cuts worth an extra £6bn."
He added: "The SNP's scare stories on the NHS are the biggest lie of the campaign. The health service in Scotland is fully devolved. Only the First Minister can privatise the NHS here or cut the budget. Spending on health has increased in recent years. Even SNP Health Minister Alex Neil has now admitted that."
Figures from the UK Government show the proportion of the NHS budget spent on private providers in 2013-14 was 5.9% - compared to 2.8% in 2006-07. It claims increasing competition is focusing on who can provide the best quality of care and includes not just private providers - with the NHS and charities also able to tender for contracts.
The Scottish Government spends the equivalent of around 1% of the NHS budget on private healthcare, which it has said is used mainly to help meet waiting list targets. Concerns have been also raised the NHS across the UK could be impacted by a new EU-US trade deal, known as the Transatlantic Trade and Investment Partnership, which would allow public services to be open to private competition.
Alex Neil has said he has written to the UK Government to make it clear the health service must be excluded from the negotiations. A UK Government spokesman said: "The NHS is a national treasure for the UK, which will always be there for everyone who needs it, funded from taxation, and free at the point of use. There is an NHS constitution for England which sets out that health services are based on clinical need and not an individual's ability to pay."
He added: "Spending on healthcare from private-sector providers only equates to around 6% of total NHS expenditure -only 1% more of the NHS budget now than in 2010. NHS funding in England has increased by £12.7bn over the past four years. Over the whole of this Parliament the increase to Scotland's health spending is more than £1.3bn as a result of Barnett consequentials from increases to health spending in England."