The UK is seeing an "early" third wave of Covid-19 infections which is being led by the Indian variant, Prof Gupta says.
He is member of the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag) which advsises the government, and tells the Today programme: "There has been exponential growth in the number of the new cases and at least three-quarters of them are the new variant.
"Of course the numbers of cases are relatively low at the moment - all waves start with low numbers of cases that rumble in the background and then become explosive, so the key here is that what we are seeing here is the signs of an early wave.
"It will probably take longer than earlier waves to emerge because of the fact that we do have quite high levels of vaccination in the population, so there may be a false sense of security for some time, and that's our concern."