A significant increase in infection rates in the UK is partly down to a new Covid-19 variant linked to South Africa which is "more transmissable", according to the Chief Medical Officer for England, Professor Chris Whitty.
An estimated 1 in 50 people in private households in England are estimated to have had Covid-19 as new daily cases in the UK reached a high of more than 60,000 on Tuesday.
Here's what we know so far about the new strain in the UK:
Where has the variant come from and where has it spread in the UK?
Mr Hancock said that two cases of the new variant were first identified in the UK last month.
"Both are contacts of cases who have travelled from South Africa over the past few weeks," he said.
The virus spread extremely rapidly in the Eastern and Western Cape outbreaks in South Africa and is now the dominant strain there. At around the same time it was identified in the Eastern Cape, cases were identified in Kent.
Those with the new coronavirus variant in the UK, and contacts of them, were quarantined.
However, the variant was then identified in cases in London and the south-east leading to the increase of restrictions in those regions to Tier 4 before Christmas.
By Christmas, samples of the variant were found across the UK including areas of Scotland, Wales, the North East and the Midlands.
Professor Whitty said Covid-19 hospitalisations across England are now "rising very rapidly" adding that the new variant is in the east of England, London and south-east, and is "now taking off in other areas as well".
What is different about this new variant?
The new variant is deemed to be more transmissible than the UK one, which was already classed as being more prolific than the original coronavirus.
ITV News' Science Editor Tom Clarke said: "The South Africa strain shares one mutation with the UK strain called 501Y: a potentially crucial one on the bit of the virus’s 'receptor binding domain' that might help it grab onto our cells and infect them.
"But it has several other potentially important mutations that are completely different from the ones the UK strain has evolved."
How infectious is it?
Similar to the other UK new strain which was confirmed in December, but has been in the UK since September, this variant is also "more transmissible".
Mr Hancock added: "This new variant is highly concerning because it is yet more transmissible and it appears to have mutated further than the new variant that has been discovered in the UK."
Latest figures suggest the South African strain was behind a record number of people being hospitalised there.
The virus spread extremely rapidly in the Eastern and Western Cape outbreaks in South Africa and is now the dominant strain there.
Is it more infectious for children?
Chief Medical Officer, Professor Whitty said it is not thought the new variant is more dangerous for children and young people.
He said: "One thing that we do not think is that this new variant is any more dangerous for children than the old variant is.
"There’s no evidence, for example, that the hospitals are filling up with children.
"There is always a risk with any infection to people of all ages but children are relatively much less affected than other groups, which is one of the few good things you can say about coronavirus, and that will be important obviously when schools can go back."
Will the variant have an effect on the vaccine?
The Government's Chief Scientific Adviser, Sir Patrick Vallance said it is possible the South African coronavirus variant may have some effect on vaccine effectiveness but is unlikely to “abolish” their effect.
He said that a possible change in the virus shape in the variant “theoretically gives it a bit more risk of not being recognised” by the immune system.
“There is nothing yet to suggest that’s the case. This is being looked at very actively,” he said.
“It’s worth remembering that when a vaccine is given you don’t just make one antibody against one bit, you make lots of antibodies against lots of different bits, and so it’s unlikely that all of that will be escaped by any mutations.
“But we don’t know yet.
“At the moment, you’d say the most likely thing is that this wouldn’t abolish vaccine effect. It may have some overall effect on efficacy but we don’t know.”
Is travel affected?
Last month, the Government restricted travel from South Africa and urged those who have been in contact with anyone who had recently been in South Africa to quarantine.
But the health secretary said that these were temporary measures while the new strain was to be analysed at Porton Down.
Mr Hancock added: "We are incredibly grateful to the South African government for the rigour of their science and the openness and the transparency with which they have rightly acted as we did when we discovered a new variant here."
The Prime Minister has faced calls to strengthen border protections to prevent the arrival of new cases, particularly of new and concerning strains.
But he made no mention of the border during his address to the nation on Monday evening, when he ordered schools in England to close in enacting the toughest lockdown since March.
What have experts said about the new strain linked to South Africa?
Infectious diseases expert Dr Susan Hopkins told a Downing Street press conference: "The new variant in the UK which we’ve identified is very different to the variant in South Africa, it’s got different mutations.
"Both of them look like they are more transmissible. We have more evidence on the transmission for the UK variant because we’ve been studying that with great detail with academic partners."
She added: "We’re still learning about the South African variant and you’ve heard already the measures that we’re introducing to ensure that we quarantine people who are coming in from South Africa.
"Therefore, we are pretty confident actually that this system we have in place will help control the spread."