I found this in the roofspace whilst laying additional insulation. Looks like the previous occupants had taken a trip back in June 1976 ( the year afer British Airways was formed from BEA and BOAC ).
As best I can transcribe it:
23 JE 1976 BRITISH AIRWAYS AIRPORT COACH SERVICE W.L.T. TO HEATHROW AIRPORT 90P ADULT NOT TRANSFERABLE ???
WLT is the railway code for Wallington Station, SW6.