In a slick corporate training room in L'Oreal's west London headquarters, young hairdressers are surreptitiously changing the answers they had previously given in questionnaires as they watch a soothing video with a salon-style soundtrack.

The surprise topic for the first 20 minutes of their workshop is not hair colouring techniques but basic facts on HIV/Aids: how the disease is spread, and how it is not; how it can be treated, and why it should not be a taboo.