So did I, but website shows (and this is dated May 2007):

miles earned on bmi
fare type no of miles earned applicable classes UK and Europe applicable classes longhaul routes
business fares & premium economy x 2.0 c, d, j, y c, d, j
standard - mid economy x 1.5 s s, u, l, y
standard - economy x 1.0 b,k b, k m, h, o, q, v, w, e
standard - discounted economy x 0.5 m, h, q, v, g, o, w, t, n,e
tiny fares & special promotional x 0.25 all tiny fares g,t,n