They use the ADEXP to determine which part of the route is in the UK. Because the auto generated points are ATC area handover points. So this data is the best w

They use the ADEXP to determine which part of the route is in the UK. Because the auto generated points are ATC area handover points. So this data is the best way so see which part of the route is within the UK airspace. Then it needs to find the ICAO part that corresponds, because the controller needs to use the ICAO plan that the pilot has. If the controller sees other (auto generated) waypoints that the pilots don't have you get problems during operation. A simple example is that controllers can tell pilots to fly in a straight line to a specific point on their filed route (and do so quite often). The pilot is expected to continue the filed route from that point onwards. They can also tell a pilot to fly direct to some random other point (this also happens but less often). The pilot is then not expected to pick up a route after that point. The radio instruction for both is exactly the same, the only difference is whether the point is part of the planned route or not. So the controller needs to see the exact same route as the pilots have, not one with additional waypoints added by the IFPS system.