Good Morning Britain hosts Alex Beresford and Charlotte Hawkins spoke to Dr Sarah Jarvis on Wednesday's show, as she warned Tier 3 just cannot combat the new strain of Covid-19.
The new strain, which began in the South East, has now spread across the country and Dr Sarah believes tougher restrictions, such as those seen in Tier 4, will be needed to stop the spread and the pressure on the NHS.
Her warning comes as the country saw its highest daily increase in case on Monday with 33,364, and 190,000 new cases in the last week.
Dr Sarah said she "feared" Tier 3 restrictions were not enough for the new strain, which brings the R rate up by 0.4, from around 0.8 to 1.2.