Measures for containing the spread of Covid-19 would still hold for the fast-spreading strain circulating in Britain, which may show up in more cases here, unless it gets loose in the community, said infectious disease experts.

So far, there is one confirmed case with the more contagious B117 strain in Singapore, a 17-year-old Singaporean who arrived from Britain on Dec 6.

There are at least 13 others with positive preliminary tests for the strain, including a Singapore Airlines pilot and a work pass holder returning from Britain.

"The community does not need to be particularly worried about (the new strain), especially if people continue to practise the individual safe management measures such as mask wearing and social distancing," said Professor Teo Yik Ying, who is dean of the National University of Singapore's (NUS) Saw Swee Hock School of Public Health.

Professor Ooi Eng Eong, an expert in emerging infectious diseases at Duke-NUS Medical School, said current control measures should suffice as the British variant is still spread mainly through respiratory droplets.

But Associate Professor Alex Cook, vice-dean of research at the Saw Swee Hock School, said "things may change if we start to see transmission of the English variant that we can't nip in the bud through contact tracing and testing".

The B117 strain is reportedly 70 per cent more contagious, but has not shown signs of being more lethal or severe. A British analysis found that the variant is linked to a higher viral load in respiratory samples, which may be why it is more transmissible.

Singapore has instituted travel restrictions against Britain, forbidding all long-term pass holders and short-term visitors who have been there within the last 14 days from entering or transiting through Singapore.

From Monday, the same restrictions will apply to travellers from South Africa, where another potentially more contagious strain is circulating.

Asked if there was a need to revise the stay-home notice beyond 14 days in the light of the more contagious strains, experts said that this was not necessary as there are only a few people who turn up with the infection after the quarantine period.

Prof Ooi said balancing case prevention and costs is needed to keep public health measures sustainable. "Catering to extremes of incubation period and unusual cases would make Covid-19 prevention in Singapore even more costly," he added.

Prof Cook suggests increasing the number of tests for those on quarantine instead.

To protect the country against more contagious strains, 90 per cent or more of Singapore's population may need to be vaccinated.

On Thursday, Britain reported 55,892 Covid-19 cases, its highest daily total for the year, mostly driven by the new variant.

Experts said the virus has been mutating since the pandemic, but most mutations have not affected transmissibility.

Infectious diseases specialist Leong Hoe Nam said: "The virus is only interested in world domination. It is in the virus' interest to mutate to a milder strain or a strain that is more transmissible, instead of one that will kill the host."

Places that have large outbreaks offer more fodder for the virus to mutate.

Professor Gavin Smith, interim director of Duke-NUS Medical School's emerging infectious diseases programme, said the best way to stop new variants emerging is to stop outbreaks of Covid-19, so the work on Sars-CoV-2, the virus that causes it, must continue.

He said: "Most mutations are what we call 'neutral' - they don't change the virus' behaviour.

"But occasionally, there will be mutations that change the virus' behaviour in unpredictable ways. So it is important that public health agencies and scientists remain vigilant and keep track of any new variants that might emerge."