Police have been asking to see our tickets (or, since the obvious route from the metro to the collection point is through the cordoned area, our confirmation emails). Bit bureaucratic but it means the square is pretty much exclusively Albion.
I hope this doesn't help anyone (in that I hope nobody ends up needing this kind of help) but I see that there's a British Consulate in Marseille at 10 Place de la Joliette so that's (a) easy to remember and (b) handy.