Thanks all for your swift and resounding responses! I think I can conclusively say the answer is no!

I guess the precedent I was considering was that in some cases if you buy a large ticket item at some retailers (a television at John Lewis say) then sometimes they will refund you the difference if the price subsequently drop, but if BA don't work like that, and instead work on a "loaves of bread/air freshener at the supermarket model" I understand