Thanks for the info guys. So AutoEnginuity recommended I buy their ST06 plus the 'BMW and Mini enhanced interface', which would have totalled £367/$480 - too much for a one-off DIY job. I bit the bullet and paid £162/$212 for my local Mini dealer to do it for me (they called it a DSC bleed). It improved the brake pedal but it still isn't as expected disappointingly. As a last ditch attempt I'm going to replace my discs as they are a few years old then pressure bleed the system once more. Fingers crossed.