This november 5th just gone, we were on final approach to 27L at LHR in A320 and at about 250 - 300ft we were hit right on the nose by a firework!! Wasn't so much dangerous to the aircraft but it gave both of us up front a hell of a shock and it certainly distracted for a good few seconds. Thankfully the autopilot was still in (just), if it hadn't been the pax would have got a wee bump at I lept out of my seat with fright. The bang was so loud once landed the cabin crew were straight on the interphone reporting it. What would possess someone to do this I don't know, did prove how vunerable LHR and other airports are that someone can hit a landing aircraft with fireworks!!!