"In order to reduce the risk posed by British nationals and return home residents, we will require all arrivals where entry cannot be refused to stay in isolation in government-provided hotel accommodation. They will be received at airports and transported directly to quarantine," he told MPs.
The tightening of the rules will be detailed later by Home Secretary Priti Patel.
At stake is the risk of new infections with more dangerous variants of SARS-CoV-2, the virus responsible for Covid-19, such as those first detected in South Africa or Brazil.
In addition to these two countries, the measure is to be applied to a further 20 countries, including Portugal, Cape Verde, Angola and Mozambique, as well as Argentina, Chile, from which direct flights are suspended and visitors are banned due to close links with South Africa and Brazil.
Thus, British and UK residents arriving in England from countries potentially affected by the variants are subject to this system, such as Portugal and most southern African and South American countries due to close relations with Brazil and South America.
Since 15 January direct flights from Portugal, Cape Verde and 14 South American countries have been suspended by the UK to avoid the arrival of cases with a new variant of the virus detected in Brazil, which is considered very contagious.
The UK had already banned direct flights from South Africa and other African countries such as Angola and Mozambique in December, and the entry of passengers due to the risk presented by a new strain of SARS-CoV-2, called 501Y.V2, also considered highly infectious.
Arrivals from these countries are already prohibited, except for British and foreigners with resident status, and all have to present a negative result of a diagnostic test performed up to 72 hours before.
Under the current containment regime, all unnecessary foreign travel, such as tourism, is prohibited and the Prime Minister said that exit checks would be increased and people could be prevented from crossing the border "if they do not have a valid reason".