Transport blocks! Car is just over a year old and had an occasional clunk sound at low speed going over bumps, which now I'm back in the UK with it is really noticeable given the plague of aggressive speed bumps and potholes here. Rang local dealer Pentagon Chilwell to try and get it looked at, and over phone their workshop manager diagnosed it as possibly some transport blocks being left in the suspension. Took it in today and 15 mins later he was holding them in his hand. I really can't believe that this car was delivered to me and has been in for two recalls and a service in Spain without anyone noticing they hadn't finished prepping it. Fwiw, he said this is something they've found before in cars from other dealers, so if you've got a clunk on a new car (and the suspension is pretty firm), get it looked at.