Johnson said the British government is taking "every possible step" to find a coronavirus vaccine.

Joining the prime minister for the press briefing, the government's Chief Scientific Adviser Patrick Vallance said coronavirus infections have been spreading from younger to older people, leading to increased hospital admissions, especially in northern England.

But he said 40 percent of people in hospital currently are under the age of 60.

Asked about whether a "circuit breaker" lockdown would save more lives than the regional tier approach, Vallance said the government has to take various factors into consideration, including the economy and mental health.

However, he did admit that even the highest level of the Tier Three restrictions are "not enough" to tackle the virus and further actions could be needed on the worst-affected areas.

Britain's coronavirus reproduction number, also known as the R number, has edged up slightly, the latest government figures showed Friday.

The government's Scientific Advisory Group for Emergencies (SAGE) said the R number is now between 1.3 and 1.5, up from last week which was between 1.2 and 1.5.

The R number is one of many indicators scientists use to determine how fast COVID-19 is spreading in the country. If the R number is above one, it means the number of cases will increase exponentially.

Another 15,650 people in Britain have tested positive for COVID-19, bringing the total number of coronavirus cases in the country to 689,257, according to official figures released Friday.

The coronavirus-related deaths in Britain rose by 136 to 43,429, the data showed.