2002 XJR Loud ticking when push loud pedal

Hi everyone greetings from a very hot South Africa. The XJR overheated after being stuck in bad traffic. low water had shown before I started off but on checking level was fine. warning light stayed on but foolishly took the car out. home journey about 1 hour because robots (traffic lights) out all over so heavy conjestion. Temp guage stayed normal! Stalled very close to home but managed to get going again after a few min’s but then the noise! At first thought I had picked up a plastic bag underneath but as I was only minit’s from home carried on got to gate stalled again this time i could smell that burning like old fashioned clutch slipping smell. would not start so rolled in. left for a short while that’s when temp showed super hot and fans kicked in, gentle push of the pedal and sound of loud ticking from left bank area. Obviously serious and what comes to mind is maybe a valve seat dropped and is pined behind a valve? Can anybody think of any other causes? I will investigate further but would be greatful if sujestions would point me in what direction I might go before engine out and big money looms!!! Many Thanks Guys Hope to hear comments Regards Dave B