Last night whilst listening in to London ATC West (132.95), at around 2105z, I heard an aircraft call in (out of Exeter) call sign Quality 969E (not certain if that's the absolutely correct c/s) at FL160, requesting urgent clearance to descend to FL100, which was immediately granted and ATC instructed them to Dover reporting point and asked if they wished to declare an emergency (my first thought was that a passenger was taken bad - heart or breathing problem) - to which the reply was Negative at this time. About 2111, they declared Mayday - which AFIK means a serious defect with the a/c itself. They were granted immediate clearance to go direct to Gatwick LGW and emergency services would be alerted. I think they were directed to fly over Mayfield? They were then hand over to London ATC, and I heard no more - did anyone else hear anything, or does anyone know what the the emergency was, or what happened at LGW?