Originally Posted by jchand

When Tesco first won the Airmiles contract you received 400 BA miles of 40 Airmiles for each £2.50 voucher. If you were a premium Clubcard customer with an average spend of £60 a week They would double the conversion to 800 miles of 80 Airmiles.

Tesco then decided to improve the redemption levels to 600 BA miles an 60 Airmiles for each £2.50 clubcard voucher and do away with the premium qualification. However they grandfathered premium customers at the old 800 / 80 rate.
So even with the reduction to 500/50 it is still better than the original deal.