From listening in, the crew did not seem overly concerned about inspections etc. from the Fire Service after landing - taxied clear of RW and quick low key chat on 121.6, then taxied on. ATC did however say they had declared a Mayday...
If it was even a Fire indication I would therefore think it went out pretty quickly
LHR ATC as ever "coped" v well - a quick additonal orbit or 2 here there and everywhere to let him slot in... Just as well - gave BA a chance to get dispatchers to stand and guidance on
