Boddingtons,

When you make your bookings on flybmi.com and get through to section 4 (the summary) it will give you a break down of the fare basis. The class this is booked in will depend on the level of miles you receive, standard fares earn anything from 50%-150% and the amount of miles for each class is shown on the 'earning page' of the diamond club website or your earning and spending booklet you received when you upgraded to gold.