The loss of taste and smell is a strong single indicator of Covid-19 infection, more so even than a cough or fever.

Until Covid struck, anosmia – the medical term for a loss of smell - was relatively rare, although it was known to affect people with viral infections, and other conditions such as head injuries. For most people, this unwelcome phenomenon will be mercifully brief but for a minority the virus causes nerve damage. The good news is that the nerves can regrow. It just takes time, anything from two months to two years.

One of the worst effects is being unable to enjoy food and drink, as it's the sense of smell that allows you to taste "flavour". In some cases, relationships can even break down – not least because humans are hard-wired to use smell in determining the attractiveness of a partner.

There are, however, things you can do to help with the recovery process. It works because humans have around 400 smell receptors: the training helps you to "turn on" these receptors, which in turn helps to stimulate your olfactory nerves as they repair.