Interline on BA is ID 80. Roughly speaking, when all taxes and charges are added to the final price, it works out at about a 50% discount on an equivalent firm ticket with the airline.
£1750 is the max amount of concession available and had not changed in 20(?) years. The cost of holidays in the meantime has roughly doubled. Sadly you are not able to use the maximum amount of concessions on an increasing amount of hotels in the group (platinum, small and friendly etc) so, like with a number of other things, it is a diminishing benefit.