The new variant of coronavirus sweeping London and the South East has spread to other parts of the UK, a public health leader has warned.

But Dr Susan Hopkins, of Public Health England, said that while many regions had cases of the new strain, these were in much smaller numbers than in London, Kent and parts of Essex.

She told Sky’s Sophy Ridge On Sunday: “It has been detected in many other parts of the country.

“Every region has cases but with very small numbers.

“It has also been detected in Wales, in Scotland, we have not had any detected in Northern Ireland.”

Dr Hopkins also said that she hoped people who had crammed onto trains out of London after Prime Minister Boris Johnson announced on Saturday the capital was one of the areas going into the new Tier 4 would reduce their contacts.

Dr Hopkins said: “I understand people’s wish to get home to their families and loved ones that they may live with on a normal day-to-day basis and wanted to get out of London last night.

“I hope that when they go to wherever they are moving to they reduce their social contacts and don’t contact anyone outside their household for the next 10 days, as that will help minimise the risk of transmission to other parts of the country.

“We know it’s in other parts of the country in small amounts but what we are trying to do is prevent more spread and rapid increases across the rest of the country.”

Her comments come after Mr Johnson effectively cancelled Christmas for almost 18 million people in London, south-eastern and eastern England as the region was put into a new two-week lockdown from Sunday.

Scientists on the Government’s New and Emerging Respiratory Virus Threats Advisory Group (Nervtag) have concluded the VUI 202012/01 mutant strain, identified by the Public Health England laboratories at Porton Down, is spreading more quickly.

Dr Hopkins said that while the new strain had been identified in October from a sample taken in September it was not until Friday that its higher transmissibility was confirmed.

When asked on Sky’s Sophy Ridge On Sunday why Mr Johnson was still insisting on Wednesday that it would be “inhuman” to cancel Christmas, she said: “We did not have the modelling evidence to show that the transmissibility was increased or that the R value was increased on Wednesday.”

The Government’s chief scientific adviser Sir Patrick Vallance warned on Saturday that the new variant was becoming the dominant strain, with a rapid rise in cases in recent days.

But Dr Hopkins said there was no evidence that the new variant of coronavirus was causing a disproportionate number of hospital admissions.

She said: “We have got no signals, so the first signals we would expect to see is in the South East where this has definitely increased over weeks now.

“But what we know is the more cases we have in the community with this virus the more cases we are seeing in hospital.

“But we are not seeing a disproportionate number of people being admitted to hospital over the last two weeks and we are not seeing any increases in mortality yet.”

Dr Hopkins said there was evidence that there was evidence of people with the new variant having higher viral loads of the virus.

But she said a higher viral load did not mean people were going to get more ill, adding: “The illness comes from the immune response and how it reacts in your lungs – that’s where we know the illness really starts to be driven from and why people need oxygen.

“The higher amount of the virus means that people are likely to be more infectious than they would otherwise be and this means we need to reiterate the social distancing measures.”

Dr Hopkins said that until further studies are carried out there cannot be certainty the vaccine will be effective against the new Covid-19 variant.

She added: “We won’t know for definite until we have further studies.

“The vaccine induces a strong, multiple response, immune response and therefore it is unlikely that this vaccine response is going to be completely gone.”

Maria Van Kerkhove, Covid-19 technical lead at the World Health Organisation, said the variant had also been identified in Denmark and the Netherlands. One case was also found in Australia, but it did not spread further.

She added: “And so more sequencing that can be done will be helpful to help us determine if this variant is circulating elsewhere.

“Sequencing will also help us understand any changes in the viruses that are being identified.”