> That would have grounded only the plane with the flight plan that the UK system could not process.
By the looks of it, it was few hours in the air by the time the system had a breakdown. Considering it didn't know what the problem was, it seems appropriate that it shut down. No planes collided, so the worst didn't happen.
Couldn't the outcome be "access to the UK airspace denied" only for that flight? It would have checked with an ATC and possibly landed somewhere before approaching the UK.
In the case of a problem with all flights, the outcome would have been the same they eventually had.
Of course I have no idea if that would be a reasonable failure mode.
By the looks of it, it was few hours in the air by the time the system had a breakdown. Considering it didn't know what the problem was, it seems appropriate that it shut down. No planes collided, so the worst didn't happen.