The Health Protection Agency (HPA) has warned that for every confirmed case of the stomach bug, there are likely to be a further 288 unreported sufferers.
There have been 2,630 confirmed cases so far this season, meaning that the real number could be 757,440.
A spokesperson for the HPA said: "Laboratory confirmed reports represent only a small proportion of the actual amount of norovirus activity in the community, because the vast majority of affected people do not access health care services as a result of their illness."
As cases of the norovirus soar across the UK, fresh guidance is issued by clinicians on how to treat the symptoms.
The number of confirmed cases of the winter vomiting bug, norovirus, is 72% higher than at this time last year, health experts have said.