: "One in five people with Covid still present with less common symptoms that don't get on the official PHE [Public Health England] list - such as skin rashes.
"Seeing increasing numbers of Covid tongues and strange mouth ulcers."
That means up to 20 per cent of Covid cases could be going unaccounted for, leaving those people more likely to unknowingly spread the virus.
He urged people to continue sending him pictures of their "Covid tongues" - when the mouth rash is coincided with fever and fatigue.
IMPORTANT SIGNS
Prof Spector has previously called for the NHS to expand its list to ensure Covid cases are spotted in the early stages.
His team were among the first to spot that a loss of taste and smell could be an indicator of the virus and successfully had it added to the official list.
Experts first said skin rashes in the mouth should be recognised as an important sign of Covid-19 back in September.
Researchers examined 666 patients at a temporary field hospital that had been set up at the peak of the pandemic in Madrid, Spain.
Experts revealed that 46 per cent of patients had some form of skin rash, with the hands and feet being particularly affected.
They also found that 26 per cent of patients had a rash inside the mouth and small bumps were the most common signs.
Gabriel Scally, a public health physician and president of epidemiology and public health at Royal Society of Medicine, told The Sun: "Symptoms in the mouth have been described for some time in association with Covid-19.
"It is such a problematic virus to treat as it produces effects in such a wide range of body systems."
Prof Scally said: "The medical name for an acute swelling of the tongue that occurs as part of a syndrome is 'glossitis'.
"It can also involve discolouration and can also be known, more popularly than medically, as 'strawberry tongue' or 'raspberry tongue' in these cases.
"It can occur in a wide range of conditions."
Certain diseases that affect the immune system may attack the tongue, including herpes.
Changes in the tongue, including pain, discolouration, swelling or a strange texture, are sometimes the result of an underlying condition.
But they can also be the result of poor mouth hygiene, smoking or an unhealthy diet.
A white or "furry" tongue is often caused by coating of debris, bacteria and dead cells.
But it could be a sign of a health condition, for example oral thrush, and the NHS advises seeing a GP about it.
Mouth ulcers are very common and can be caused by a range of things, including hot food or drink, medicines, stress, hormonal changes or vitamin deficiencies.
Patrick Vallance says lockdowns have worked to slow things down but warns 1 in 55 still have Covid