Key word is "signatories." This is the same mistake that lefties make when talking about the "Geneva Convention". The Geneva Convention, like the Constantinople Accord, apples only to those countries which have actually signed it (hence inoperative in either Iraq or Afghanistan, e.g.).<p> And in WWI, the British effectively shut down the Canal to use by the enemy.
It's also interesting to note that Britain shut down the Canal in World War I -- in explicit violation of the 1888 treaty -- by establishing a formal British Protectorate in occupied Egypt.
It's also worth noting that when Col. Gamal Nasser nationalized the Suez Canal for Egypt in 1956, the U.S. ended up siding with Egypt against both Britain and France (and Israel, too) -- mainly because Nasser expressed his intention to abide by the "open access" terms of the 1888 agreement. So in that case we saw a bizarre "strange bedfellows" situation where the U.S., the Soviet Union and Egypt -- none of whom were signatories to the 1888 accord -- ended up enforcing the terms of the 1888 accord against two signatories of that accord (Britain and France) as well as a former colony (Israel) of one signatory.
Go figure.