Howdy Alan, I found this link thru a google search: 4D modelshop Ltd Shop - Primers it showed this info:
Hycote Acrylic Red oxide 150ml
Reference: FP20006
Hycote brand
I also found this info, but since I dont have much experience with humbrol paints, not sure if it is acrylic or enamel, but here it is:
humbrol red brown 70 + matt scarlet 60= red oxide
hope this helps,
Greg