Re: And this is why the Aussies are on top of it
"Instead, everyone will Eurostar it to Brussels or Amsterdam and fly from there."
The quarantine is for people coming TO the UK. I've not seen anything about quarantining people leaving FROM the UK.
Having said that, we won't, yet, be quarantining people from Ireland or France. So I suppose people coming to UK could fly into either of those places and then use Eurostar to get here. I suppose that depends on whether Ireland or France are going to be quarantining incomers, however they arrive and whether the UK will be at least checking who arrives from France/Ireland by ferry, tunnel or plane and how/when they got to France/Ireland