Simon Cornwell gives dates of the Stanton 6 and 7 from the 1930s. Click on the 7b link and see examples in Salisbury which appear to be late 1940s with the larger bases.
The 6B was "modified" in the 1950s went it became more streamline in the base probably to reduce costs and weight. The 7 was probably redesigned around the same time.
There are roads in Salisbury where both the big and slimmer base Stanton 7s are used with the slimmer ones perhaps replacing older (cast iron?) columns like what may have happened your way. I haven't found any decent pre 1950s pictures of Salisbury side roads to confirm.
There are however loads of 1950s pictures on the web of Salisbury City centre and these show big based Stanton 6Bs but also 6Cs and a few 6Gs.
OIder pictures do show cast iron (gas?) columns prior to that.
Thanks for that info Phosco. It seems that in the 1950s Stanton modified their whole range, replacing some of their older columns with totally new ones and updating the design of the 6 and 7 range at the same time. This is handy for identifying the rough ages of columns in my area and, in some cases, the ages of the roads they light.
Also of note is the Stanton 10 range which was introduced in 1958. This means that some parts of Blackpool and most of Fleetwood must have had their side roads relit with these columns and fluorescent lanterns during the late 50s/early 60s as there are literally thousands of these columns in my area. Prior to this the roads must have been lit with cast-iron columns. If only I could travel back in time and see what happened!
The really interesting cases are roads which have a mixture of Stanton 7 (MKII) and Stanton 10 columns, I wonder how these were originally lit.
I remember in the 80s In Fleetwood on a road called Wansbeck Avenue (built in the 50s I think) until all the columns were sleeved every column was a Stanton 10 fitted with GEC Z8256s except for one Stanton 7 (MKII) in the middle of them all fitted with (from memory) a GEC Brookvale mercury lantern. I wonder how this came to be? The mind boggles!