Following a letter / email exchange with DC to request clarification of miles earning policies, the site has now been updated as follows:
http://www.flybmi.com/bmi/src/html/d...earnmiles.html
Please note the miles you earn depends on the airline operating the flight. In the case of codeshare flights with partner airlines, the operating carriers's miles earning structure will apply.

Somewhat bizarre given that no other Star Alliance carrier does this. But presumably BMI is free to act as it wishes.
Clarification of min miles calculations:
To calculate the total miles you’ll earn for your flight, simply multiply the above miles [taken from min miles earned on BMI table] by the factors shown below depending on the type of ticket you’re travelling on.
Car rentals: bless 'em, whoever updated the site entered too many zeros, so apparently now you get 15,000 Destinations Miles for renting a car from Budget, Avis or Hertz. Given that BMI has become such a stickler for the rules, I suggest someone makes 7 different hire car bookings next week and demands 105,000 DMs in return.

Just make sure you do a screen print of what the page says before you book!!
I've pointed out to the senior manager responsible for DC that this response fails to address the source of disenchantment among those who've posted to this board: namely that the new miles earning policy was introduced without prior announcement and that bookings made / ticketed before the changes were brought in should therefore be honoured at the old earn rates.
I'll keep you all posted. Meantime, I urge you all to put pen to paper if you want to raise any of these issues with BMI. PM me if you want the name of the person to get in touch with.