I've just come across this Spanish map from 1882 of the Eastern Telegraph Company's cables (in the Biblioteca Nacional de Espana). It's a good deal clearer than most cable maps I've been able to find, and is going to be particularly useful in the telecommunications history course I'm currently teaching.
The map suggests that the ETC, or one of its subsidiaries, operated a cross-channel cable from somewhere near Hastings to Le Harve. Does anyone know which firm ran it?
On the subject of cable maps, the ever-brilliant Distant Writing website has just posted a link to a high-quality scan of the Electric Telegraph Company's routes in 1852: