Just over a generation ago the world was in the grip of hysteria about a mysterious new disease that seemed to be spiralling out of control. Groups of men in southern California were falling prey to an aggressive auto-immune disorder which had never been seen before.

Health experts and policy makers scrambled to understand this terrifying new disease and how it could be treated and prevented.

Fast forward 40 years after those first cases of HIV and Aids and the picture has transformed: today HIV is more akin to a long-term condition than a certain death sentence and the number of new infections are declining in most parts of the world.

And governments on both sides of the Atlantic are now so confident that they have the virus under control they have both predicted that they can stop the disease in its tracks.

Last month health secretary Matt Hancock promised that by 2030 there would be no new cases of HIV in England. His Welsh counterpart Vaughan Gething made a similar pledge at the end of last year. And in his State of the Union address US president Donald Trump took many people by surprise by promising the same thing.