And if you do, you'd know that there's nothing technically stopping such solutions from being implemented. Political (and commercial) will is the problem here, although a genera
From the UK point of view, it's preferable to have the UK border as far away from the island as possible. If you'd read the 2025 Border Strategy document, you'd know that the UK is placing a lot of emphasis on partnership with industry, including having carriers provide data as required.
It's amazing how many people claim that it 'can't be done', yet this is exactly what the UK government wants to do.
Barcelona-Lyon supports two direct flights a day, for instance. But this is a commercial matter and beyond the scope of this thread. However, you have to remember that Ryanair proved that people will travel to all sorts of places if there are opportunities to do so. Barcelona-Lille might not seem like a particularly interesting journey, but Barcelona-Lyon opens up the possibilities of ski trains from Barcelona. There are many possibilities, but this is for commercial carriers to investigate.
Again, you keep talking about 'no precedent'. There was no precedent for UK border controls abroad until the signing of the various agreements that regulated the juxtaposed controls. There was no precedent for customs controls to be carried out in France before the Channel Tunnel. Now it's normal.
What security risks are there? Are we really saying that we can't trust the data provided by the Spanish authorities regarding an individual? If someone is clean in Spain and GCHQ can't find anything on them, what difference does it make if it's Pablo from Catalonia or Dave from Manchester physically sitting there?
Or you can just employ Brits on local contracts for the same money. There's plenty of Brits in Spain who wouldn't mind a normal job with normal Spanish working conditions while being employed by the UK Government.
Or they can eliminate them by operating Barcelona-Lyon-London too.
The truth is that the possibilities are there, but there's a) no commercial interest and b) no political will.