One of the mods on another section worked in Orlando airport helping with the quarantine process for flights arriving from New York and other hotspot areas in USA. For them it was the the airport which passengers departed from which was the determining factor. For example, on all flights from JFK to Orlando the passengers had to fill out the quarantine forms, irrespective of where they actually lived.
I would expect it to be the same in Europe. On all flights from Germany, all passengers, irrespective of their nationality would have to quarantine. On all flights from France, all passengers irrespective of their nationality would not have to quarantine. This is because in France, there is already a 14 quarantine procedure for anyone arriving into France.
Therefore UK, Ireland and France are basically a quarantine free bubble.