Update: UPS think they have found my MBP. They delivered it to Amazon of all places (a fulfilment centre). It is sitting in a trailer full of parcels of Amazon stock

. So, they need Amazon to unload the trailer and find my parcel, send it back to UPS who will return it to a UPS distribution hub for delivery to me. This could take up to 28 days!
At this point, I may be better asking Apple to ship out a replacement, which could be faster. Apple did say a replacement would "jump the queue" of other BTO machines (i.e. they'd build it faster), but it would still need to be shipped from China.
I understand these are difficult times, but this is pretty incompetent from UPS - delivering my MBP to the black hole of an Amazon warehouse.
Sorry, rant over