Somerville was to offer Admiral Gensoul four options with a six hour time limit:
1 Put to sea and join forces with British
2 Sail to a French W,Indies port and demilitarise his ships
3 Sail with reduced crews to any British port
4 Scuttle all his ships within six hours of this offer.
Gensoul failing to opt for any of these choices,Somerville was ordered to destroy the ships at Mers el Kebir,particularly Dunkerque and Strasbourg. Somerville was further ordered to destroy the warships in the port of Oran itself,if this will not entail any serious loss of life.
The meting you mention was in his flagship HMS Hood.
Source Barnett's "Engage the Enemy more Closer"