VUI-202012/01 is a new strain. Transportation into France via the Chunnel is shut down (but unaccompanied trailers or freight containers still are allowed into Calais). I understand that normally 10,000 trucks went through the Chunnel daily. London is "Tier 4" which in effect means stay at home... one member of a household may meet with one member of another household (as I understand it).
In British terminology VUI is an abbreviation for Variant Under Investigation. This variant was first identified in December, and the new strain is involved in more than 1,100 COVID-19 infections in the UK. It has also been reported in Netherlands, Denmark, Belgium and Australia.
The UK government raised the threat level to Tier 4 in London and surrounding counties. As of midnight 12/20-12/21 it is illegal to leave the Tier 4 area, except for essential travel. Matt Hancock, Secretary of State for Health and Social Care said in a BBC interview: the goal is to "keep the virus within London." He said "the new variant is out of control", and everybody in the Tier 4 area should act as though they have the virus.
New York Governor Andrew Cuomo said on Sunday that NYC has "about 6 flights per day coming from the UK, and we have done absolutely nothing". He said the federal government should either test all UK arrivals or institute a travel ban. Currently the U.S. government bans travelers from most European countries, including the UK. But the ban does not apply to U. S. citizens returning to the USA.