Republican Chuck Grassley claimed that Ted Kennedy (above) would be left to die untreated from a brain tumour in Britain. Photograph: Steve Connolly/Rex Features

The National Health Service has become the butt of increasingly outlandish political attacks in the US as Republicans and conservative campaigners rail against Britain's "socialist" system as part of a tussle to defeat Barack Obama's proposals for broader government involvement in healthcare.

Top-ranking Republicans have joined bloggers and well-funded free market organisations in scorning the NHS for its waiting lists and for "rationing" the availability of expensive treatments.

As myths and half-truths circulate, British diplomats in the US are treading a delicate line in correcting falsehoods while trying to stay out of a vicious domestic dogfight over the future of American health policy.

Slickly produced television advertisements trumpet the alleged failures of the NHS's 61-year tradition of tax-funded healthcare. To the dismay of British healthcare professionals, US critics have accused the service of putting an "Orwellian" financial cap on the value on human life, of allowing elderly people to die untreated and, in one case, for driving a despairing dental patient to mend his teeth with superglue.

Having seen his approval ratings drop, Obama is seeking to counter this conservative onslaught by taking his message to the public, with a "town hall" meeting today at a school in New Hampshire.

Last week, the most senior Republican on the Senate finance committee, Chuck Grassley, took NHS-baiting to a newly emotive level by claiming that his ailing Democratic colleague, Edward Kennedy, would be left to die untreated from a brain tumour in Britain on the grounds that he would be considered too old to deserve treatment.

"I don't know for sure," said Grassley. "But I've heard several senators say that Ted Kennedy with a brain tumour, being 77 years old as opposed to being 37 years old, if he were in England, would not be treated for his disease, because end of life – when you get to be 77, your life is considered less valuable under those systems."

The degree of misinformation is causing dismay in NHS circles. Andrew Dillon, chief executive of the National Institute for Health and Clinical Excellence (Nice), pointed out that it was utterly false that Kennedy would be left untreated in Britain: "It is neither true nor is it anything you could extrapolate from anything we've ever recommended to the NHS."

Others in the US have accused Obama of trying to set up "death panels" to decide who should live and who should die, along the lines of Nice, which determines the cost-effectiveness of NHS drugs.

One right-leaning group, Conservatives for Patients' Rights, lists horror stories about British care on its website. An email widely circulated among US voters, of uncertain origin, claims that anyone over 59 in Britain is ineligible for treatment for heart disease.

The British embassy in Washington is quietly trying to counter inaccuracies. A spokesman said: "We're keeping a close eye on things and where there's a factually wrong statement, we will take the opportunity to correct people in private. That said, we don't want to get involved in a domestic debate."

A $1.2m television advertising campaign bankrolled by the conservative Club for Growth displays images of the union flag and Big Ben while intoning a figure of $22,750. A voiceover says: "In England, government health officials have decided that's how much six months of life is worth. If a medical treatment costs more, you're out of luck."

The number is based on a ratio of £30,000 a year used by Nice in its assessment of whether drugs provide value for money. Dillon said this was one of many variables in determining cost-effectiveness of medicines. He said of his body's portrayal in the US: "It's very disappointing and it's not, obviously, the way in which Nice describes itself or the way in which we're perceived in the UK even among those who are disappointed or upset by our decisions."

On Rupert Murdoch's Fox News channel, the conservative commentator Sean Hannity recently alighted upon the case of Gordon Cook, a security manager from Merseyside, who used superglue to stick a loose crown into his gum because he was unable to find an NHS dentist. The cautionary tale, which was based on a Daily Mail report from 2006, prompted Hannity to warn his viewers: "If the Democrats have their way, get your superglue ready."

The broader tone of the US healthcare debate has become increasingly bitter. The former vice-presidential candidate Sarah Palin last week described president Obama's proposals as "evil", while the radio presenter Rush Limbaugh has compared a logo used for the White House's reform plans to a Nazi swastika. Hecklers have disrupted town hall meetings called to discuss the health reform plans.

David Levinthal, a spokesman for the nonpartisan Centre for Responsive Politics, said the sheer scale of the issue, which will affect the entire trajectory of US medical care, was arousing passions: "It's no surprise you have factions from every political stripe attempting to influence the debate and some of those groups are certainly playing to the deepest fears of Americans. There's been a great deal of documented disinformation propagated throughout the country." Defenders of Britain's system point out that the UK spends less per head on healthcare but has a higher life expectancy than the US. The World Health Organisation ranks Britain's healthcare as 18th in the world, while the US is in 37th place. The British Medical Association said a majority of Britain's doctors have consistently supported public provision of healthcare. A spokeswoman said the association's 140,000 members were sceptical about the US approach to medicine: "Doctors and the public here are appalled that there are so many people on the US who don't have proper access to healthcare. It's something we would find very, very shocking."