So why did the RN sink the French ships in Oran, but accepted the neutrality of the French ships in Alexandria? Answer - the intransigence of the French Commander at Oran who followed the Vichy line.
For full versin read "Sailor's Oddysey", Adm Cunningham's autobiography. It contains details on all of the decisions at the time and a necessary read if you are to understand the Mediterranean War 1940-43.