Sufferers can constantly smell fish, sulphur and ‘burnt toast’

Prof Nirmal Kumar, an ear, nose and throat surgeon, said the “very strange and very unique” long-term symptom known as parosmia seemed to be affecting young people and healthcare workers in particular.

The professor, who is the president of ENT UK, the professional body for ear, nose and throat surgeons, was among the first to identify anosmia – loss of smell – as a coronavirus indicator.

After treating patients with anosmia, he noticed some were recovering only to then experience parosmia. One patient “could smell fish in place of any other scent”, another “can smell burning when there is no smoke”, he added.

“We think there is increased incidence in young people and also in healthcare workers because of exposure to the virus in hospitals.

“The virus is affecting the nerves in the roof of the nose – it’s like a shock to your nervous system, and the nerves aren’t functioning.”

Patients have reported being haunted by “unbearable” odours.

Daniel Saveski, a 24-year-old banker living in London, described a burning, sulphur-like odour, or a smell “like toast”.

Lynn Corbett, an administrator for an estate agent, said: “Most things smelled disgusting, this sickly sweet smell which is hard to describe.”

Coffee, beer and petrol smelled “unbearable”.

For those trying to regain their sense of smell, AbScent, a charity that supports people with smell disorders, recommends “smell training” – sniffing rose, lemon, clove and eucalyptus oils every day for around 20 seconds.