=> My grandson's Harry Potter loco cab has become distorted =>following a fall from the tabletop. (Don't ask!) Can anyone advise =>how best to tackle this and what material is used for the moulding =>of these models ? => Quercus.
AFAIK, they're made of polystyrene plastic.
As for repair - depends on the amount of damage. You may have to cut it off, and replace it with a 3rd party part -- if there is such a thing. It might be possible to temporarily remove the bent and broken portions, scab in bits of sheet plastic underneath, and glue the bent and broken bits back on. Use plastic filler (such as is made for the model airplane crew) to fill gaps, sand smooth with very fine sandpaper, repaint ... Bit of a chore, eh? But probbaly worth it. :-) If the damage is minor, just bending things back into place, and gluing sheet plastic underneath might be enough.
An alternative might be to find a junker engine with the same or similar cab at one of the shows, and just swap cabs. Would cost a bit, but again, might be worth it.