.........I don't know about Staverton, but they did operate in and out of Luton. It may or may not have been a home base, but I recall seeing and hearing on RT what I took to be a Viking there a few times. It may have been on a calibration job, but routine calibration was normally carried out by 'Ministry' Doves as far as I recall. Cranfield a bit North was the sort of place for that kind of activity as well.
The reason that I remember is also that one blue sky day I was trundling peacefully around Hertfordshire in a Chipmunk, and met this Viking (Valetta? ) coming the other way. We were both VFR, but the Smiths driver grumbled that I was on his patch. I took early action to ensure that I kept well out of his path, but this still involved some further muttering on the phone later on. Maybe there was a notam out. I was about 18 at the time, so it was probably my fault. At that time, Luton, Hatfield, Radlett, and Elstree were fairly active and not all that far apart. Somewhere I have a photo taken at Luton that records a Canberra, Tiger Moth, and 749 Connie sharing the ramp. ( maybe it was called the dispersal in 1961)
Quite a few PPRuNers will have done courses with Smiths at Cheltenham. Mine in 1965 was for the amazing Smiths Flight System as fitted to the Britannia. ( still my favourite )
You could even do an auto-coupled ADF approach, but I don't remember anybody ever trying it. There was a fancy new one with real coloured bits for the Trident they kept talking about. I expect our course was about three days tacked onto the six weeks at Filton, but I think the school was more set up for deeper courses for the engineering and maintenance side.
My last years were on the 744 with more geeky novelties than a Samsung Android, but that 1950s vintage Smiths was so smooth and just as cool. Who thought up that trick of rotating the main compass system indicator so that your present heading and track info was at the bottom?.........brilliant...never a dull moment on ab-initio circuit training if it started to get boring.