Why are you getting so excited about BA doing this? It is, imho, a pre-emptive move because if it was not for BA doing the route, some other airline, probably a Silverjet/EOS/L'Avion-style company, would have done it sooner than later now that also the CFM-powered A318 has been certified.
The whole ballyhoo about getting the A318 certified for LCY was certainly not about Air France or Lufthansa flying the A318 to Paris or Frankfurt - it was more about getting it as a biz jet and for potential long-hauls into the docklands.