thank you - so appears that schengen arrivals in europe are treated in the way domestics are handled in the UK and also the US?

because in my experience at most UK airports (unlike european airports) i've found that there isn't really an 'exit' once you're in departures - it's a one-way system. Also intl pax could hypothetically purchase duty free items and give to arriving domestics, thus circumnavigating the system. This is why in the US they hold onto your duty free when youve purchased it and give it to you at your gate when boarding the flight.

Hey - just to clarify: are you saying that at those airports mentioned above, no-one could have flown in from LHR or Bristol or somewhere else in the UK?

I am not sure what you mean. But to clarify, for those airports like EDI, they do not segregate domestic arrivals from all the departing passengers. Why would you need to?

yes they could have flown in from elsewhere in the uk, including lhr and bristol

Any uk domestic flight arrivals can enter directly into the departure area if the airport is set up to do that.

schengen arrivals in the schengen countries in europe and uk domestic arrivals in the uk are treated in the same way, they can enter directly into departures, no need to reclear security.

I am not so familiar with the US, it may be similar

Lhr, lgw and stansted are like that, but ncl, gla, edi, abz, all mix domestic arrivals with departing pax and there are exits from the departure area.

Hypothetically an international pax could buy duty free and then just leave the airport with it and put it in their car or give to a friend and then reclear security and get on their plane.

You could do it even at airports with no direct exit from the departure area.

I am sure if it was believed to be a big problem then a system similar to the us system could be introduced.

That said, owing to baggage being collected at final destination in the uk (unlike the us where you collect bags and clear customs at point of entry) there are customs protocols in domestic arrival areas even off domestic flights. So it may not be as easy as it sounds.

They hypothetically could. But I can't imagine it would be a profitable way to organise smuggling at scale. Any taxpayer losses here would be marginal at best.