Scientists warned only mandatory hotel quarantine for all travellers to the UK would come close to fully preventing the import of new COVID variants, it has emerged.

The government last week announced plans for UK nationals and residents returning from “red list” countries to be placed in quarantine in government-provided accommodation – such as hotels – for 10 days.

However, this action will stop short of a full closure of the UK’s border, or mandatory hotel quarantine for all arrivals, as some had called for.

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It has now been revealed that on 21 January, almost a week before the government announced their plans, the government’s Scientific Advisory Group for Emergencies (SAGE) warned that “reactive, geographically targeted” travel bans “cannot be relied upon to stop importation of new variants”.

They said this was “due to the lag between the emergence and identification of variants of concern” as well as “the potential for indirect travel” to the UK via third countries.

However, the scientists did say the emergence of new COVID variants around the world meant there was a “rationale for attempting to reduce importation of even small numbers of infectious cases”.

The emergence of the SAGE advice comes amid fears the South Africa coronavirus variant, believed to be more contagious than the original variant, is spreading across England.

Prime Minister Boris Johnson announced the plans for mandatory hotel quarantine for those arriving from “red list” countries to MPs last Wednesday.

But ministers have yet to reveal when the plans will be put into practice.

The UK’s travel “red list” currently consists of 33 countries and includes all those in South America, as well as large parts of southern Africa and Portugal.

Last week, the United Arab Emirates was added to the list and a ban on direct flights was imposed.

Labour’s shadow home secretary, Nick Thomas-Symonds, reiterated his call for border measures to go further following the emergence of the SAGE advice.

“These revelations are incredibly serious,” he said.

“Ministers have knowingly left the UK border open and potentially exposed people to new strains of the virus, in direct contradiction of their own government scientists’ advice.

“This puts the gains of the vaccine at risk, with disastrous consequences for people’s lives.

“The home secretary (Priti Patel) needs to come to parliament urgently and reverse this reckless policy of leaving our Borders unlocked and open to further risk.”

The prime minister was recently accused of having overruled Ms Patel after she claimed she argued for the shutting of the UK’s borders at the start of the COVID-19 pandemic last year.

Those calling for tougher border measures have frequently pointed to the examples of Australia and New Zealand, who have imposed mandatory hotel quarantine since the early weeks of the pandemic and have largely eliminated transmission of the virus within their borders.

There have been 105 cases of the South African variant detected in the UK – and 11 of them identified over the last five or six days do not appear to have links to international travel.

This has led to concerns there may be pockets of spread in local communities with the health secretary announcing a testing blitz of 80,000 people aimed at finding “every single case”.

The eight postcode areas at the epicentre of the intensified testing programme are: Hanwell, west London; Tottenham, north London; Mitcham, south London; Walsall in the West Midlands; Broxbourne, Hertfordshire; Maidstone, Kent; Woking, Surrey; and Southport, Merseyside.