Britain could discover within “a few days” whether vaccines work against new mutant coronavirus.
Scientists are growing the new variant at a Porton Down military base before testing whether antibodies can prevent it infecting cells.
The verdict is crucial to prospects of a return to normal life from Spring.
Scientists said NHS records will also flag up within weeks if those already vaccinated are going on to contract the variant, known as VUI- 202012/01.
It has now been reported in five other European countries after evolving in south east England.
Countries have barred Brits from entering after data suggested the variant out-competes its predecessor and spreads 70% more.
Scientists said they have seen no evidence yet that vaccines will be significantly less effective against the variant.
Prof Peter Openshaw, of Imperial College London and past president of the British Society for Immunology, said: “It’s clearly important that all of this is tested.
“People are working away in the labs as we speak, to try and get some preliminary answers at least within the next few days.
“But this is not quick science as you have to wait to grow the virus. This should come out in the next few weeks.”
Cases of Covid-19 involving the new coronavirus variant observed in Britain have been reported in at least three other countries in Europe.
The European Centre for Disease Prevention and Control made the announcement in a “threat assessment” that a few cases have been reported already by Iceland, Denmark and the Netherlands.
It also cited media reports of cases in Belgium and Italy.
The EU agency urged health authorities and labs to monitor for the new variant’s spread and alert other EU countries about new cases.
Crucial testing is now being carried out at a number of labs including the UK’s military testing centre at Porton Down, Wiltshire.
It involves growing the mutant virus in a container, then adding antibodies known to prevent disease in standard Covid-19.
It will then be observed to see if the antibodies stop the virus infecting the cells.
If they do not then vaccines may need to be re-engineered, delaying widespread national protection from against coronavirus.
Prof Adam Finn, of Bristol University, said “If you substitute a virus that we’ve already got in the lab, and we know that virus can be prevented from infecting cells, with the new variant virus and use the same antibodies you can then see if there’s a difference.”
He added: “We will have evidence on that in the relatively near future and that’s clearly a matter of immediate interest and importance. Time will tell.”
There are fears that Britain could endure lockdowns for months of 2021 and vaccines are seen as the main hope against them.
Prof Stephen Evans, drugs expert at the London School of Hygiene and Tropical Medicine, said: “We can not only do things in the lab.
“We actually are in an unprecedented situation and we have the ability to monitor the effectiveness of the vaccine in its rollout.
“We have in general practice records and hundreds of thousands have been vaccinated already and that’s going to go up dramatically over the next week or so.
“We’re going to be able to look in those records and see who gets Covid.”
It is estimated that the new variant could boost the reproduction rate – known as R – by 0.4.
When R is above 1 the outbreak is increasing. If it is below 1, it is decreasing.
Government adviser Prof Calum Semple said Britain should not “beat ourselves up” about the new variant developing here.
The Liverpool University professor and Sage member said: “When it comes down to the genomic work on the virus and the research and understanding of how the disease is behaving, we are a world leader in this field.
“We shouldn’t beat ourselves up about this evolving here.
“The fact is we’ve identified it, we’ve brought it to national attention, we’ve got the attention of the politicians and the World Health Organisation in very quick time.”
He added: “We do not yet have herd immunity despite those people that think herd immunity is going to be the salvation.
“We won’t have it until a very large number of people have been vaccinated.”