Joining the likes of Sid_Goon, LimeJellyTeddy and Flopsydaisy in tweeted outrage might once have been considered beneath the dignity of a prime minister. But Gordon Brown has defied convention to add his voice to a burgeoning Twitter campaign to defend the NHS after US Republicans labelled it "evil" and "Orwellian".

"PM: NHS often makes the difference between pain and comfort, despair and hope, life and death. Thanks for always being there," tweeted Downing Street. He was followed by an even keener Twitterer, Sarah Brown, who said: "#welovetheNHS – more than words can say."

The Browns added their Twitters to thousands of heartfelt declarations from patients, nurses and other medical practitioners on Twitter's #welovetheNHS topic. Such was the popularity of the campaign to defend the NHS from Republicans highlighting the so-called dangers of a "socialised" healthcare system that the micro-blogging site crashed on Wednesday.

If it was an unusual move for Brown to join an online campaign, the prime ministerial Twitter also challenged the convention that British governments do not wade into domestic political battles in the US.

As well as support Obama's healthcare reforms against Republican attacks, the Browns have personal cause to praise the NHS. The prime minister's sight in one eye was saved when he lost the other in a teenage rugby accident, the Browns' son, Fraser, has cystic fibrosis, while they publicly thanked NHS staff for the support they received when their first child, Jennifer, died in 2001.

The Labour presence on #welovetheNHS highlighted the relative absence of senior Conservatives, despite the eagerness of David Cameron's team to embrace new methods of communicating with voters. Daniel Hannan, the Tory MP whose anti-Brown speech went viral on YouTube this year, joined Republican criticism of the NHS on US TV earlier this week, saying he "wouldn't wish" the NHS "on anyone".

Perhaps Cameron was wise to declare he did not agree with Hannan and his party was "100%" committed to the NHS without resorting to Twitter. As the intervention by Andy Burnham, the health secretary, showed, politicians' attempts to match the informality and passion of ordinary Twitterers can look silly.

A Twitter posted on his 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."

Eschewing football for greater formality, Burnham said – rather than Tweeted – later: "I am exceptionally proud that Britain has a world class NHS which treats people on the basis of clinical need – irrespective of their ability to pay. The groundswell we have seen on Twitter … is testament to its remarkable achievements."