Top-up fees in the National Health Service may sound harmless—surely if patients pay the additional cost of treatments not available on the NHS, they benefit without causing anyone else harm? But explored more carefully this simply is not the case.

Firstly, treatment within a publicly funded NHS should not provide what patients want, but what they need. Need for a treatment implies capacity to benefit from that treatment,1 which means that the treatment must be effective. Within scarce NHS resources, there is also a requirement for treatments to be cost effective and to provide value for money, and it is this requirement that creates the rationing problem in health care. Treatments that offer a relatively small benefit or a low probability of benefit may be worthwhile to an individual, but collectively they have an opportunity cost, in terms of other uses …