Leaving aside the impact on the airline and travel industries for a moment (and I am not being dismissive of that at all, btw, it will have a disastrous impact) but it's just another half-baked policy that can't really be implemented and relies on people abiding by the rules, because 'the population has done brilliantly so far'.
I wonder how much time our police forces will have to send an officer around to a house to check? And if the recent traveller is not there, how do you prove it? I mean they could just say they were sleeping and didn't hear. It's only a warning anyway to start off with - sorry, it's "encouragement" to do the right thing.
Michael O'Leary (and I can't believe I am quoting him) has just been saying how it's 'bonkers' when you can arrive at Heathrow, and travel on the tube (and presumably other modes of transport across the whole country) before you get to the place in which you are going to self-isolate.
Given that the travel industry is going to be massively hit by this, at least make the policy tough enough to actually work, otherwise the government is adding another nail to the tourism coffin for possibly negligible gain.