The government has reported the highest daily number of coronavirus cases in more than a month – as a quarantine for arrivals from Luxembourg was announced.
A total of 846 new cases of COVID-19 were reported on Thursday, the highest UK total since 28 June (901 cases).
A further 38 people have died across all settings after testing positive for coronavirus, taking the official death toll to 45,999.
The 14-day self-isolation requirement for arrivals from Luxembourg has been reintroduced across the UK from midnight on Thursday following a rise in cases in the country.
It comes days after the UK reintroduced the same restrictions for those returning from Spain.
The decision has provoked an ongoing row, with Transport Secretary Grant Shapps saying the government "had to act".
In the wake of the move, Prime Minister Boris Johnson has warned there are signs a "second wave" is surfacing in Europe.
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Health Secretary Matt Hancock has echoed this, telling Sky News earlier he is "worried" about another spike of infections, with a "second wave starting to roll across Europe".
Ireland reported 85 new cases of the virus on Thursday, its highest daily total in more than a month.
Meanwhile, health authorities in France reported 1,377 more cases on Wednesday.
This brings the rolling seven-day average above the 1,000 threshold for the first time since May.
Speaking earlier on Thursday, Boris Johnson said coronavirus is "bubbling up" in up to 30 areas across the UK.