For France, blaming the defeat on a regional minority will make no sense (can you imagine Germany pinpointing defeat on Westphalians, or people from Hanover?).
Blaming it on the Jews - possible, particularly if the war is presented as the consequence of big business issues. The Action Française will have a field day telling how the hated Jews and the despicable Republic are the ones to blame, after which it'll split in rival Legitimist and Bonapartist factions.
Blaming it on Britain - quite likely. It is, sadly, a natural state of affairs that members of any alliance complain that other members are not pulling their own weight. People will say Britain didn't send enough troops, or didn't act swiftly enough so Germany refrained from war, etc. It's not that people deeply hate Britain, but in 1918 only a cosmopolitan élite gets to travel and meet people from across the border. At a time when neighboring villages regarded each other in utter contempt (read La Guerre des Boutons), one can imagine the view ordinary people from different countries could have of each other. The French farmers are bound to see the neighboring farmers as scoundrels, the French soldiers as uniformed scoundrels, and British soldiers as foreign unformed scoundrels, which is arguably worse.