Short version: Are there separate (COVIS 19) rules for travel between the UK and the Netherlands, and Belgium or France, based on the mode of transport, (flights or ferries and trains.)
Long version: My long distance relation boyfriend and I usually meet each other a few times each year, him traveling to continental Europe (the Netherlands, Belgium, France) or me from the Netherlands to the UK and the other coming to the same place.
We select our mode of travel based on convenience, cost and a bit of environmental concern.
In these COVID 19 days we wonder whether there is a difference how quarantaine (or self isolation) rules work between the different modes of transport.
As we are each citizen in our own country, visa rules do not matter to us, but for completeness sake, if there is a real difference that can be included.
At the time of writing, there seems to be a huge difference in cancelation rates, with flights being cancelled more often than they happen but as I expect changing the quarantaine rules to change that, I want to keep that out of this question. I may ask a different question if it seems relevant.