The coronavirus variant first discovered in the United Kingdom could be more deadly than the original, Boris Johnson has said.
The UK prime minister revealed on Friday there was "some evidence" to suggest a higher mortality rate among those with the variant, while he assured vaccines would be just as effective.
At present, the majority of COVID-19 cases in England and Northern Ireland are that of the variant.
Speaking from Downing Street, Johnson said: "There is some evidence that the new variant may be associated with a higher degree of mortality. It's largely the impact of this new variant that means the NHS is under such intense pressure."
It was already widely accepted that the UK variant, first found in Kent, was 70% more transmissible than the original - but figures on the mortality rate hadn't been available until now.
Scientists estimate variant B117 could be around 30% more lethal, although chief scientific advisor Sir Patrick Vallance has warned this conclusion is "not yet strong".
"I want to stress that there's a lot of uncertainty around these numbers and we need more work to get a precise handle on it, but it obviously is a concern that this has an increase in mortality as well as an increase in transmissibility," he said.
In December, this transmissibility factor resulted in all four governments of the UK being forced to cancel plans for a relaxed Christmas as cases initially skyrocketed in London and the southeast.
A third national lockdown was eventually announced in January, with no real date for when restrictions would let up. In fact, Johnson this week suggested lockdown could continue into summer.
The new restrictions come as Britons continue to look in horror at the record-breaking case numbers and deaths being reported day-upon-day.
Nearly 2,000 people died in the 24 hours to Wednesday evening. Another 1,401 were recorded on Friday.
Numerous countries have also tried to block the spread of the variant themselves, although some of these efforts have been in vain.
Those countries in the EU reporting the variant include: Austria, Belgium, Cyprus, Czechia, Denmark, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Luxembourg, Malta, the Netherlands, Poland, Portugal, Romania, Slovakia, Spain, Sweden.