Boris Johnson has said the UK can look forward to a "very different world" after Easter as he sought to ease growing concerns over a new variant of Covid-19.

The Prime Minister addressed the nation on Monday evening amid fears that the UK risks being effectively cut off from parts of Europe due to the variant.

He said the Government took “prompt and decisive” action when the mutant variant was discovered in the UK on Friday, with much of the country entering Tier 4 lockdown restrictions.

In Scotland, areas on the mainland are set to enter level four of the country's tier system on Boxing Day.

Boris Johnson also confirmed that more than half-a-million people in the UK have now received their first dose of the coronavirus vaccine.

The first ever dose of the Pfizer jab was administered to British grandmother Margaret Keenan on December 8.

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The Government’s New and Emerging Respiratory Virus Threats advisory group (NervTag) told a Science Media Centre briefing on the new mutant variant that cases outside of Tier 4 in London and the south east of England “are increasing at similar rates” those in affected areas, and that it had a “transmission advantage” over other strains of the virus.

However, World Health Organisation director-general Dr Tedros Adhanom Ghebreyesus said there was “no evidence” the new strain was “more likely to cause severe disease or mortality”.

Elsewhere, regional public health directors in Manchester and the West Midlands urged anyone who travelled from a Tier 4 area or Wales to self isolate upon their arrival and “assume” they have the new Covid-19 variant.

Speaking at a Downing Street press conference on Monday evening, after crunch talks involving members of the Cobra emergency committee to prevent the UK being cut off from the continent in the days before Christmas, Mr Johnson said discussions were taking place to “unblock the flow of trade as fast as possible”.

He said: “It was an excellent conversation with the French President (Emanuel Macron), he stressed he was keen, I would say, to sort it out in the next few hours if we can.

“Our teams will be working on it flat out – if we can get a result then, that would be great, but we will do it as fast as we can.”

Transport Secretary Grant Shapps urged people not to travel to Kent amid the closure of the French border.

He told the press conference: “Please don’t travel to Kent.

“Most people should be staying at home, everybody in Tier 4 must at stay home and in Tier 3 stay very local.”

Referring to the vaccine, Mr Johnson said: “I can today announce that over half a million people, more than 500,000 people in the UK, have now received their first dose.”