Just days before its 60th birthday the NHS is being forced to re-evaluate its founding principle - that treatment is based on clinical need not the ability to pay.

The issue is whether patients should have the right to “top up” NHS care with their own funds. It has been pushed to the fore by The Sunday Timesand a Conservative MP representing a constituent who was told during her terminal illness that she would forfeit the right to state-funded healthcare for that condition if she paid for cancer drugs which the NHS would not provide.

The Department of Health was right this week to announce a review of the top-up ban. While policy reviews can often be a smokescreen for inaction, this issue is complex, emotional and does not lend itself to a quick fix.

The fear is that ending the ban would open the door to two-tier healthcare, with the state offering a minimum service and the rest being available to those who could afford it.

The horror would be two patients in adjacent beds receiving different treatments because one had more money - precisely the opposite of the guiding principle of the NHS. But modernising the rules around top-ups need not be a dagger to the heart of the NHS. The review, being carried out by cancer czar Professor Mike Richards, could find a formulation that relaxes the rules for a small range of cases but continues to bar the use of private cash for the vast majority of patients.

The number of people wanting to pay for top-ups will always be small - mainly people seeking access to drugs the NHS deems not to be cost-effective.

It should be remembered, however, that these patients may have unrealistic expectations of the benefits they will derive from their expense - they must not be allowed to fall prey to exaggerated claims.

The current rules hurt only those of relatively modest means, not “the rich”. Those with great wealth are fine - they can afford to go entirely private as the rules dictate. It is the patients who could scrape together a few thousand pounds to pay for a drug but who could never pay for the whole of their treatment who are caught by the top-up ban.