Have they delisted?
Aviation Week (American magazine) dated 14th Sept page 12 "Market Focus" quotes closing price on Sept 9th - BA Current Week 34.96; Previous Week 29.50; Trailing /E 14.0 Fwd P/e 9.7 Pct Chg YLD 35.3 up.
Other airlines listed include Jetblue Southwest and Air Tran, all of which are not listed on the London FTSE. So I reckon BA are still listed on the NYSE.
BD