England’s Chief Medical Officer Chris Whitty on Saturday announced that the United Kingdom has identified a new variant of the coronavirus, which “can spread more quickly” than prior strains of the virus, prompting Prime Minister Boris Johnson to impose fresh restrictions on parts of the country, reported Reuters.

London said it had informed the World Health Organization of its findings, according to BBC.

“As announced on Monday, the UK has identified a new variant of Covid-19 through Public Health England’s genomic surveillance,” Whitty said in a statement. “As a result of the rapid spread of the new variant, preliminary modelling data and rapidly rising incidence rates in the South East, the New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG) now consider that the new strain can spread more quickly.”

His warning followed a meeting of representatives from the UK’s four nations to discuss the new strain.

The United Kingdom has reported roughly 24,061 new Covid-19 cases every day, based on a weekly average, which is a more than 40% increase compared to a week ago, according to a CNBC analysis of data compiled by Johns Hopkins University. The country reported 20,10,077 cases and 67,177 deaths as of Sunday.

Public health officials told BBC that the new variant, which has been identified and is known as VUI, was first seen in mid-September in London and Kent. By December, it had become the “dominant variant” in London.

“In London, data over the past week suggests the new variant has accounted for more than 60% of new cases,” Whitty told CNBC. “So what this tells us is that this new variant not only moves fast, it is increased in its ability to transmit, but it’s becoming the dominant variant. It is beating all the others in terms of transmission,” he said.

Yet there is “no evidence” that the new strain causes a more severe disease, more hospitalisations or “more trouble than the other virus”, Whitty added.

In a press conference, prime minister Johnson said the new strain “may be up to 70% more transmissible than the old variant” although there was no evidence it was more deadly or led to a more severe illness.

“We’re learning about it as we go, but we already know enough, more than enough, to be sure that we must act now,” he added, as he announced new restrictions to contain the spread of the disease, according to CNBC. “When the virus changes its method of attack, we must change our method of defence.”

Tougher measures were announced for London, south east, and eastern England. The planned relaxation of Covid rules for Christmas was also scrapped for large parts of south-east England and shortened to just Christmas Day for the rest of England.

Johnson announced the creation of a new tier – Tier 4 – in the Covid-19 alert system for towns and areas in England, according to the Hindustan Times. London, which till now was in Tier 3 with the strict restrictions, was moved up to Tier 4, the highest level of curbs.