It's La Manche
Both countries use metric system - Britain doesn't appear to do so, by all planning, building, engineering is done in metric system units. A road sign needs to be 200 meters before the junction. But it needs to indicate distance in yards. The result is that not a single road sign in the UK is correct
Anyway, there wasn't really much standardization there. As for the trains, British simply had to go for whatevere French side had to offer. German trains for the Eurotunnel will need to conform to Eurotunnel specs.





