A new strain of Covid-19 has been identified in the UK.
The fast spread of the variant has led to the introduction of tighter coronavirus restrictions across the four nations, and many countries across the world enforcing travel bans from the UK.
It has also been linked with the exponential rise in coronavirus cases in the south-east of England, with experts saying the new variant is more transmissible than others.
Here’s everything you need to know about the new strain - and whether you should be worried about it.
What is the new strain?
Matt Hancock told MPs on Monday 14 December that a new variant of Covid-19 had been identified, and that it was spreading in some areas of the country.
The new strain was first detected in September, and in November around a quarter of coronavirus cases in London were the variant. Now, it accounts for nearly two-thirds of cases in the city.
The World Health Organisation was notified about the virus change, Mr Hancock said, and scientists had commenced analysis on it.
Where did the variant come from?
It was first detected back in October, by the Covid-19 Genomics UK Consortium (Cog-UK).
The new strain was found in two samples, collected from Kent in London, on September 20 and 21.
Virologists suspect that the multiple mutations happened in a patient with a severely suppressed immune system, who may have had the virus for weeks and then infected someone else.
Is it more transmissible?
The new sprain has spread quickly in London and south-east England, becoming the dominant variant.
It was responsible for 62 percent of infections in London during the week ending 9 December, and it’s now present in Scotland, Wales and throughout England.
As it has spread quickly, scientists believe it could be more transmissible - either that or people were ignoring Covid restrictions and allowing it to spread.
Computer modelling has suggested that the new strain could be 70 percent more transmissible than other variants.
That was the figure Boris Johnson referred to when speaking about the new strain - and he said that could increase the R number - the infection rate - by at least 0.4.
However, Professor Neil Ferguson said there was “strong evidence” that the new variant is 50 percent more transmissible than the previous virus.
Can it infect children more easily?
The new variant could infect children more easily, said Professor Neil Ferguson, a member of the government’s New and Emerging Respiratory Virus Threats advisory group (NervTag).
He said there is a “hint” that the virus has a “higher propensity” to infect children, according to the latest data.
Prof Ferguson explained: “What we've seen over the course of a five or six-week period is consistently the proportion of pillar two cases for the variant in under-15s was statistically significantly higher than the non-variant virus."
However, he warned that more data would be needed before a conclusion could be made.
Can a test detect the new strain?
Standard Covid-19 swab tests - which are now widely used at testing centres across the UK - will be able to detect the new virus variant, England's Chief Medical Officer, Professor Chris Whitty, said.
However, it is too soon to know exactly what the new strain will do to the behaviour of the virus.
Can it cause more serious symptoms?
There is currently no evidence to suggest that the new strain of coronavirus can cause more serious or different symptoms to other variants.
However, if the new variant means more people are infected more rapidly, that would subsequently lead to more people being hospitalised.
As scientists undertake studies of and collect additional information about the new strain, they will be able to determine whether it is linked to any differences in symptoms.
Will it respond to a vaccine?
Despite the detection of the strain in multiple areas of England, Matt Hancock said clinical advice had so far suggested that it would be “highly unlikely” the new strain would not respond to a vaccine.
And BioNTech chief executive Ugur Sahin told Bild TV he was confident that the Pfizer/BioNTech vaccine would be effective against the new strain – but that his company would still be looking into the variant over the coming days.
The vaccines invented by Pfizer, Moderna and Oxford all train the immune system to attack the spike protein of the virus - which is where the mutation has been found.
Yet, the human body learns to fight off multiple parts of the spike, which is why health experts have said the vaccine will still work against the new strain.
When the mass vaccination programme really kicks off and lots of people are given the jab, the virus will have to mutate again in order to try and infect those people who have been immunised.
A regularly-evolving virus could lead to multiple updates of the vaccine - just like what happens with the flu jab.
What is a mutation?
A mutation is a change in a virus’s genome, which is the set of genetic instructions that house all the information the virus needs to function.
Mutations happen when the virus makes contact with a host and starts to replicate.
The set of instructions is then copied, but mistakes can often happen in the process.
Where the errors occur within the genome will determine whether they have a positive or negative impact on the virus’s ability to survive or replicate.
SARS-CoV-2 is a RNA virus, which is more prone to mutations, unlike DNA viruses, like smallpox.
As it has passed from person to person over the past few months, Covid-19 has been, and continues to be, mutating.
Should we be worried about the new strain?
Matt Hancock said there was “nothing to suggest” that the new strain would be more likely to cause serious illness, although he urged the public to be “vigilant” and follow the rules and restrictions in place to ensure the spread does not increase.
The good news is that mutations are a part of the natural process of an RNA virus and are very common.
Since the coronavirus started to spread across the world, it is thought that it has been mutating twice a month to find the most effective way to infect humans.
Sometimes, a virus mutates in a way that makes it worse at infecting people - and the new strain can then die out.
However, the new strain could affect how fast the virus spreads between people, which could explain why levels of the variant are higher in the places where there are more cases.
Scientists will be analysing its behaviour to determine whether it really does spread faster than the existing versions of coronavirus.