I believe the tail plane from the desert was used as a spare for mods. to allow the whole thing to be changed and then the removed one to be modified without grounding any aircraft.
The first fins and tail planes were built at Hurn. I remember seeing them when I used to go into work with my father on a Sunday afternoon in the early 60's.
I was about 8-10 years old.
The last of the Viscounts and the first One-Elevens were also being built.
I don't think this would be allowed now.
And I've just seen a Super VC-10 fly over my house near Yeovilton.
It was going north at about 10,000ft, inbound to Brize I presume.
Still looks wonderful!