The day this started I did the following:
Changed the front brake discs
Filed down the edges of the front brake pads so they don't need a hammer to get them into the callipers
Removed the strut brace (to change the rear spark plugs and clean the inlet manifold)
Given how often I have had the subframe off the car, I strongly suspect it was the latter which caused the clunking as not knowing any better, I remove the strut brace with the front wheels off the floor, causing the strut tops to disappear down into the wheel arches...

I've replaced the drop link. I've shoved the suspension/arb bushes around with a pry bar with no noticeable movement and I've re-seated the strut brace with the front wheels on the ground
Any ideas?