There has been some discussion on the Land-Rover Series One email group about the configuration of the Hardtops fitted to Home Office vehicles, and whether or not they were standard 'Export Specification' units. The following is not intended as an authoritative answer, but would seem to be as complete as basic research would suggest:
The hardtops fitted to certain Civil Defence vehicles (such as the 'Reconnaissance' ones) were fitted with windows in the sides. This was a very unusual configuration in the UK, where Purchase Tax regulations meant that a side-windowed top would normally attract tax, and so be ludicrously expensive when compared with a blank-sided top. There WERE vehicles with side windows, of course, but they had added-value station wagon configuration (with a side-hinged rear door, and ‘Alpine Light’ windows in the curved side of the roof panel itself) that would justify the added cost. But because Home Office vehicles belonged to the Crown (who didn’t have to pay tax), they could have whatever window configuration they wanted!
Indications are that the hardtops fitted to Crown vehicles were standard Export ones — confirmation from owners of Series 1 Hardtops in other parts of the world show a common side window size of approximately 10"/250mm high and 36"/910mm long. The tailgate window is about 9"/230mm x 27"/685mm. This compares with the Station Wagon side windows of 13"/330mm high (which match pretty closely the height of the front door windows). The SW rear door is the full side-hinged one,with a similar height window.
Note that only the SW appears to be fitted with small rear quarter windows (again 13"/330mm high) on either side of the door, and that these windows were not fitted as standard on non-SW hardtops. Many vehicles may have been fitted retrospectively with SW ones to improve rear visibility, but these were not a Solihull standard. This is confirmed by the 54-57 Parts Book which shows UK vehicles with no windows at all (apart from the tailgate), but with the 10" windows shown in the side panels marked 'For Export Only'. Station Wagons had windows in both the sides and rear quarters — the sides were pictured larger than the export ones (and had a different part number), with both rear and sides filling as much of the respective panels as possible. After all, the back seats were for sitting in, and the windows for looking out of!
Interestingly, both hardtops have a Tropical Roof shown (optional for the non-SW?), but only the SW has the Alpine windows.
One email correspondent suggested that early Ser2s were also without the additional small rear quarter windows, which seems to show that Solihull weren't into extra rear visibility until (say?) 1960. Incidentally, these windows in a post-Ser1 vehicle are different of course — because of the sloping sides of the later hardtops the windows don't have parallel vertical edges. All windows are also much neater fittings, without the prominent rubber surrounds.
So I think that we can take it that Ser1 hardtops with rear quarter windows but no side ones have had SW ones retro-fitted to improve rearward visibility. Also, ex-Crown vehicles in the UK (like the Civil Defence RGCs and SXFs) had the standard export side windows fitted in the factory, but with no Purchase Tax due.
But if anyone knows different, please contact me on email@example.com.