Every so often a story comes along that unexpectedly sheds light on a far more widely shared unease. Top-up payments is one of those stories. For many years we have lived, more or less happily, with a simultaneous headline commitment to an NHS that is free to all on the basis of need, an implicit recognition that rationing of health care resources in some form is necessary, and a drive to make the NHS more responsive to consumer choice.

This has run alongside a growth in the private provision of health care, either directly to the consumer, or under contract to the NHS. Occasionally questions were asked about whether these approaches quite fitted together, but few people seemed to notice. Most of us, not being philosophers, are happy enough to live with a certain amount of incoherence: life just seems to be like that. Then an issue like this crops up and you begin to realise that it might be time to check the philosophical plumbing: our categories seem to be leaking all over the place.

A certain amount of mixing and matching of private and NHS treatment has long been allowed. Where the providers could be kept separate – where the NHS does its bit and the private sector does the other bit – all was well. Some may have argued that it was unjust, but it wasn’t visibly unjust and as a result few expressed great concern. And then someone who was very ill quite understandably asked to pay the NHS to deliver a drug that NICE had said no to because it wasn’t sufficiently cost effective. The request was refused, the case made the headlines, and a number of submerged conflicts broke into the light. So what exactly lies behind the furore?

The NHS is widely regarded as a paragon of distributive justice. Funded by direct taxation, it takes according to an individual’s ability to pay and gives according to their health need. It is blind to all other differences between individuals: paupers and oligarchs are assessed with the same clinical eye. But, and this is where its starts to get philosophical, if resources are limited, if the NHS cannot provide all available treatments, its commitment to equity comes at a cost: the cost of prohibiting the freedoms of those who want to top up their treatments privately. And, as the news stories made clear, the cost is a real one. Very sick people were asking to pay for treatments that could potentially extend their lives. If they were willing to meet all the additional costs, why should their freedom to choose be inhibited?

Permit top up payments though and it looks as though equity will suffer. The sight of two equally sick people lying in neighbouring beds being treated differently on the basis of their wealth is enough to make the strongest politician blanch. Not only is there a risk of injustice, there is a risk of visible injustice.

To me this looks like a genuine dilemma: two fundamental human goods are in conflict and somehow we have to make a choice, or more probably a trade-off, between them. And as for philosophy, well it may not be able to provide an answer to the dilemma – that will be one for our consciences – but at least it can help us to understand the nature of the problem.