The UK’s National Health Service reaches 60 this week, and the celebrations have been moderated by a more melancholy reflection on past achievements and future challenges as it moves towards what would normally be the age of retirement.

If many of the basic tenets of the system remain in place, with its principle of “free at the point of use”, it continues to be subject to intense self-questioning and frequent political tinkering, including the latest NHS Constitution that was unveiled on Monday by Lord Ara Darzi, the health minister and surgeon.