Michael O'Leary of Ryanair rightly pointed out that anyone flying in will leave the airport and get straight onto a train, tube, taxi or bus, passing through transport hubs and maybe not making their way straight to the quarantine address without visiting a few other places first. This is not quarantine.
A billionaire who will lose money because of self-isolation, doesn't want self-isolation? Hmmm.
Fact is, this self-isolation once you get here process has been happening all over the world, and in the UK before 'lockdown' - which one of these do you think would produce less transmissions?
One journey from the airport to the home and then self-isolate for 14 days.
The journey from the airport to the home and then go out whenever you want.
The idea isn't to magically get to 0 infections overnight. The whole point of any measures that have been taken is to lower the amount of interactions & transmissions as much as possible. What would be the point of quarantine centres? It wouldn't make any logistically/financial sense.
To the next point, they said that there would be random spot checks. They hope that the vast majority of people will follow the guidance anyway.