You will not hear that in BrE. We don't say "five May". We always use the ordinal "the fifth of May" or "May the fifth" and just occasionally "May fifth" though that still sounds very AmE to my ears.
I think it's a quirk of our usual way of writing May 5, 1818. We'd say "May [the] fifth, eighteen eigheen for that, but when we run into the way the rest of the world writes it, we're more likely to say "five May."
I think it's a quirk of our usual way of writing May 5, 1818. We'd say "May [the] fifth, eighteen eigheen for that, but when we run into the way the rest of the world writes it, we're more likely to say "five May."