Almost everything emerging from Hitachi Newton Aycliffe and CAF Newport is imported (electrics, bogies, diesel power packs etc).
But the same is also true of output from Alstom Derby.
UK suppliers do supply various smaller parts to all the UK assembly plants, and bodyshell welding is available at Newton Aycliffe and Derby.
Hitachi and CAF can build you the same train in multiple locations (eg classes 802, 196).
The MTU power packs for class 80x bi-modes are made in Germany at a plant owned ultimately by Rolls-Royce.
It's a global world.