Complex sentence: Despite the station's name, no international services call there, however, the National Rail platforms are served by domestic Southeastern trains on the High Speed 1 route originating at St. Pancras, with interchange to the Eurostar at either Ebbsfleet or Ashford.
Split into simpler sentences: Despite the station's name, no international services call there. The National Rail platforms are, however, served by domestic Southeastern trains on the High Speed 1 route originating at St. Pancras, with interchange to Eurostar trains (which are international) at either Ebbsfleet or Ashford.