The mystery of the delivery that never happened has finally been resolved, though not without a certain amount of personal embarrassment.
I was concerned that the package hadn't been delivered because Elecraft had incorrectly addressed the parcel, so I sent them an email asking them to confirm the shipping details. I received a reply that contained an address with the house number and street name missing, an incorrect phone number and an obsolete email address that had one letter missing so it wouldn't have worked even had it still been available. Faced with evidence of such apparent incompetence, I replied with a rather blunt email telling them to sort out their mistakes, and followed it up with a rant on the Elecraft reflector.
This morning I received an email from Elecraft saying that the full address had been on the shipping label, but had for some reason failed to copy correctly into the email. Just as I sent my reply, a correctly addressed letter arrived in the post from Parcel Force stating that they were holding a package at their depot pending payment of the customs fees (VAT.) So the address apparently had been correct, and they had not attempted to deliver the package at all.
From one of the more polite replies to my reflector rant I learned that Parcel Force records that it attempted delivery on the USPS tracking site when it sends the letter asking for payment of the tax. I didn't know this, so I believed that they had attempted to deliver it to the wrong address. Elecraft had then confirmed my belief by informing me (incorrectly) that they had addressed the package in such a way that Parcel Force had been unable to deliver it at all, and were probably just about to send it back to the USA marked 'undeliverable.'
It has all been a bit embarrassing in hindsight. At the time, though, being given to believe that Elecraft had made four separate errors in the shipping details for my order seemed to justify a rant about falling standards of service.
I don't know why it takes so long and costs so much to order things from Elecraft. You can buy things from eBay sellers in Hong Kong and your purchase arrives in half the time the postage is half the amount, and very often it even escapes the attention of the tax collectors.