A total of 25 coronavirus variants are "under monitoring", Public Health England's strategic Covid-19 response director has told MPs.
She also revealed that eight variants were "under investigation", along with 25 that are currently being monitored.
The variants under monitoring appear to be higher than the most recent briefing from PHE on June 11, which suggested that 13 variants were under monitoring, eight under investigation and five variants of concern.
But Dr Hopkins said all variants had mutations that her team were concerned about.
But she said that mutations alone were not enough to predict whether it’s going to “impact on our journey through vaccines and impact on the public health risk of hospitalisation.”
She also explained how every variant that does not go “extinct very rapidly” is either going to have a “transmissibility advantage or an immune evading advantage”.
Speaking on the Delta variant, which derived from India, Dr Hopkins told the committee if it was “unmitigated”, the R number could become “greater than five and maybe up to seven”.
R is the average number of people that one infected person will pass the virus on to.
Her comments come as the UK reported 9,055 new cases, the highest daily total since February.
There were also a further nine coronavirus-related deaths in the latest 24-hour period, according to the latest government data.
The figures compare with 7,673 cases and 10 deaths announced on Tuesday, while 7,540 infections and six fatalities were recorded this time last week.