Here's the baffling info from the DC web page:

All bmi UK domestic flights and partner flights of less than 600 miles in distance: 600 miles earned for each one way
All bmi non UK domestic flights of less than 800 miles in distance: 800 miles earned for each one way
All bmi flights of more than 800 miles in distance and non bmi flights of more than 600 miles in distance travelled: 1 mile earned for each mile travelled

Means you get 600 miles min for everyone else and..
.. 800 min for BD-only non UK domestic flights
Er, what BD domestic flight is non-UK?
Or do they mean international, excluding UK domestic?

Now what about say LH in M or H class, that's a generous 0.5 miles earning - does that mean a minimum of 0.5 x 600 ?