Boris Johnson has said anyone arriving in the UK will be asked to take a PCR test in a bid to combat a new variant of coronavirus.
The Prime Minister told a Downing Street press conference on Saturday that travellers must also self-isolate until they provide a negative test result.
The measure has been set out after two cases of the Omicron coronavirus variant were detected in Britain.
Sajid Javid said there would be targeted testing in Chelmsford and in Nottingham where the cases were found.
Malawi, Mozambique, Zambia and Angola have also been added to the red list in a bid to combat the variant.
At the press conference, Boris Johnson said: “We’re not going to stop people travelling, I want to stress that, we’re not going to stop people travelling, but we will require anyone who enters the UK to take a PCR test by the end of the second day after their arrival and to self-isolate until they have a negative result.
“We need to slow down the spread of this variant here in the UK, because measures at the border can only ever minimise and delay the arrival of a new variant rather than stop it all together.
“We will require all contacts of those who test positive with a suspected case of Omicron to self-isolate for ten days regardless of your vaccination status.”
The Prime Minister added that face covering rules in England will be “tightened”, urging people to wear masks in shops and on public transport, however this will not be extended to hospitality settings.
In Scotland, face coverings are mandatory in most public places including shops, restaurants, bars, public transport and places of worship, however there are medical exemptions in place.
People are also being urged to take up booster appointments when offered to them and to also insure they are fully vaccinated.
Johnson said: “We need to bolster our protections against this new variant.
“We don’t yet exactly know how effective our vaccines will be against Omicron but we have good reasons for believing they will provide at least some measure of protection.
“If you’re boosted, your response is likely to be stronger so it’s more vital than ever that people get their jabs and we get those boosters into arms as fast as possible.”
As news of the new variant spreads, the Prime Minister said he was “confident” that the festive period would be “considerably better than last Christmas.”
Johnson said: “We continue to be in a strong position largely thanks to the speed of the vaccine rollout, another booster rollout and I think I’m going to stick with the formula I’ve used before, which is I’m pretty confident to absolutely confident this Christmas will be considerably better than last Christmas.”