Just like Spain, Luxembourg has been demoted from the quarantine exemption list published by the UK Government. Anyone arriving from yesterday will now have to self-isolate for fourteen days.
This is what GOV.UK had to say:
“There has been a consistent increase in coronavirus (COVID-19) cases per 100,000 of the population in Luxembourg since the end of June, with over a tenfold increase in total cases over this time period.”
The FCO has also advised against all but essential travel to the country. This guidance applies to all nations of the UK.