Phone call again from VW UK this morning with the only notable piece of information being that they're closing the case. I haven't heard back from the dealer either. Decided that I'm going to replace the parts myself, and attempt to cure the knock that way. Not what you should be doing for a car that is in warranty, but VW UK don't seem to care anyway.
Shock absorber to suit DCC, complete top mount with bearing already on the way. Will also be changing the control arm bushes, the drop link, the ball joint and the subframe bolts for good measure.
Will be writing to VW once it's fixed, but I suspect they'll do bugger all again, it's less "Customer Service" and more "Warranty Refusal" from my recent experience.