Problem resolved !
It turned out to be the front left
top mount.
It's genuinely what I thought it was just from sound/feel alone but until Mon I didn't realise why until I put my hand up and past the coil to feel where the tabs were located from the top spring perch/bearing and top mount itself.
Obviously it was my own installation error that caused this part to fail. Essentially it wasn't lined up to the fin at the bottom of the shock (ie towards the body of the car), and I hadn't torqued the nut correctly when the springs were compressed.
So the metal washer parts at the top of the mount ripped out of their plastic housing (I'll try and upload a photo).
I ended up replacing the shock, bump stop, top mount/bearing.
The not so old shock is fine but just kept as a spare now.