I had another fruitless conversation with Parcelforce Coventry yesterday. Despite platitudes, they admitted to not having completed a search 5 days on and on being pressed, would not commit to a date when that would happen.
I am as convinced as I can be that they want to know the contents so they can prioritise the effort, with winemaking supplies being low. The vendor is now out of stock.
I've since re-ordered from a another vendor and it arrived by courier a couple of days later.
My preferred outcome would be to receive the lost parcel, so let's see how long Parcelforce can spin this out.