Only a few days ago the dear old NHS was playing a bizarre bit part in the vicious drama surrounding healthcare reform in America. Testimony to grave defects in NHS provision popped up on the whole gamut of the US media, from mainstream television advertising through to Twitter, as opponents of reform harnessed adverse experiences from Britain to their cause.

Among the stars of the rolling anti-reform show was the Conservative MEP Daniel Hannan – a loose cannon in any context – who described the NHS as a "60-year mistake" that he "would not wish on anyone". A small parade of aggrieved British former patients followed, some of whom now say they were misrepresented.

By mid-week, offended Britons had begun a spirited fightback, spearheaded by Gordon and Sarah Brown, "tweeting" their praise of the NHS. The Health Secretary, Andy Burnham, laid into Mr Hannan as "unpatriotic". The former deputy prime minister, John Prescott, recorded a video message to the American people in defence of universal healthcare. Even the redoubtable Stephen Hawking found himself co-opted into the fray. Appearing at the White House to receive the Presidential Medal of Freedom, Professor Hawking offered a living rebuttal to scurrilous claims that the life of someone with his disabilities would be considered "worthless" in Britain's socialised health system.

All of which was vintage knockabout, part of the cut and thrust of American politics that seems so bracing when viewed, voyeuristically, from afar. Yesterday, however, everything changed. Someone else's political battle being played out at a safe distance suddenly bounced back across the water, to become potentially lethal here at home. A debate about the NHS – always likely to feature in the coming election campaign – was upon us almost before anyone had noticed.

The Conservative leader, David Cameron, tumbled to the risk that Mr Hannan's denigration of the NHS could be held against the party as a whole. As such, it threatened to discredit all his efforts to reassure British voters that the health service was safe in Tory hands. A tanned Mr Cameron emerged from his constituency residence to dismiss Mr Hannan's views as "eccentric" and pledge his troth to the NHS as his "number one priority". Just to drive home his point, he went on: "The Conservative Party stands four square behind the NHS."

If this is a rehearsal for the election campaign proper, however, there is one big drawback. The argument, as it has transferred back across the Atlantic, is about whether the NHS is a good thing. And the contest now joined by the two major parties is to demonstrate the more fervent loyalty to what Mr Cameron described as "this great national institution". But is this really the debate we should be having?

No one – except perhaps the maverick MEP Daniel Hannan – has even hinted at dismantling the NHS. But this does not mean that the service has no defects or that it cannot be improved. In the run-up to the election, there should surely be a serious discussion about how the considerable sums spent on the NHS under this government have been used. We need to know where the parties stand on its future priorities and how the cuts in public spending, widely accepted as inevitable, will be applied to the health service. These are important questions. They must not be drowned out by the clamour of scared politicians trying to outdo each other in unconditional support for the NHS as it is now.