Tory leader David Cameron said an online campaign defending the NHS from attacks in America showed how proud Britons were of the service.

Gordon and Sarah Brown were among thousands of people who posted messages of support on social networking site Twitter after the NHS was condemned by Republicans as "evil and Orwellian".

Health Secretary Andy Burnham also offered support - although he risked embroiling himself in controversy by joking he was more interested in his football team than the NHS.

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In an email to Conservative Party workers published on his blog, Mr Cameron said millions of people, including his own family, were grateful for care they had received from the NHS.

He wrote: "Just look at all the support which the NHS has received on Twitter over the last couple of days. It is a reminder - if one were needed - of how proud we in Britain are of the NHS."

President Barack Obama's plans for reforming healthcare have sparked a furious row on the other side of the Atlantic.

Opponents have warned that the changes will "socialise" the system, and could even lead to panels deciding whether the elderly deserve life-saving treatment.

Tory MEP Daniel Hannan was slapped down by his party after joining the attacks on the NHS in a US television interview last week, where he said he "wouldn't wish it on anybody".

Shadow Health Secretary Andrew Lansley said the MEP had done the NHS and Americans a disservice by presenting a "negative and partial view".

The £welovetheNHS campaign was launched by Britons keen to counter the allegations, and the sheer number of messages added apparently crashed the Twitter site on Wednesday.

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UK politicians are generally wary of wading into domestic policy rows in the US.

But among the missives was one from Downing Street stating: "PM: NHS often makes the difference between pain and comfort, despair and hope, life and death. Thanks for always being there."

Mr Brown's wife added her own comment, saying: "£welovetheNHS - more than words can say."

A message posted on Mr Burnham's behalf by Downing Street said: "Andy Burnham: Over the moon about strong support for NHS - an institution I will defend to my dying day, 2nd only to Everton FC."

Renowned physicist Stephen Hawking, who has motor neurone disease, rejected criticism of the NHS yesterday as he collected America's highest civilian honour, the Presidential Medal of Freedom.

"I wouldn't be here today if it were not for the NHS," Prof Hawking said.

Prof Hawking was commenting after one US commentator suggested he would be left to die under the UK system.

The claim, in an editorial on Wednesday for Investor's Business Daily, was later corrected after the newspaper realised that the renowned scientist was born, lives and works in the UK.

Mr Burnham said later: "I am exceptionally proud that Britain has a world class National Health Service which treats people on the basis of clinical need - irrespective of their ability to pay.

"The global groundswell we have seen on Twitter about this and the pride and strength of feeling in some of the posts is testament to its remarkable achievements."

Mr Lansley told the BBC Radio 4 Today programme that the NHS could set examples for America's healthcare system.

But he also suggested that elements of the US model could be used to improve the NHS.

Stressing Conservative "support" for the NHS and its values, Mr Lansley said: "I think it's very important for people in America to understand that the NHS has very powerful examples that they can look to.

"In this country we have a degree of equity of access to healthcare which many in America envy.

"What we need in this country, which I think Americans are very keen to retain in their healthcare system, is the ability of patients to exercise more control over their own healthcare and to make decisions about their healthcare, and to choose who provides their healthcare.

"In my view, there is no reason why the NHS in this country can't take that on board - that we can have a publicly-funded system that is true to its values but the service that's provided is far more responsive to patients."