May sound an odd suggestion but take both the wheels off and thoroughly clean the interface on the wheels and disks where the meet each other with a scouring pad or similar.
It’s something that happens on some newer cars which have a higher dynamic camber, usually on 2 piece disks but sometimes on one, where the interface sees micro movements on full lock which causes a tick.
BMW even have a service bulletin out for it where you can get friction shims fitted between the disk and the wheel!
Barrie, didn’t you have spacers and I guess spigots so the above suggestion could be it
Hi Ian, yes spacers but hub centric with 67.1mm centre bore. However, I can see the sense from the previous post from TMW as well. Cars no longer with me but have suggested new owners gets discs/pads all round. Hopefully garage will torque back up correctly on installing 
Thanks guys
Barrie
Stones trapped in caliper, they’ll fall out eventually.
Sounds suspiciously like power steering pump to me. No doubt new owners garage will sort it.
Not considered that Nigel? Must admit, only happened on full lock at low speed when pump would be at its limit. Wouldn’t be on full lock at normal road speeds so never noticed it previously.
Barrie
Just to update on this for others that may have similar issues. New owner took car to Paul Roddisons. New front discs/pads and a sticky near side slider pin has cured the issue completely.
Barrie