Speed 25 door lock configuration

Stuck in isolation I have addressed some long standing minor jobs, one of which was stripping, cleaning and re-greasing all the door mechanisms on my Speed 25 Charlesworth saloon.  After a few minor repairs I have now got everything working and in the process was surprised to find that the only external door lock is on the front passenger door.  To lock the car the driver has to move a little catch on the inside of his door to the locked position, close the door and then walk round and lock the passenger door with the key. Can anybody tell me whether this is correct, and if so what was Mr Alvis's thinking behind this rather convoluted process ?

Both my Charlesworth Speed 25 and my Mulliners 12/70 dropheads have the externally locking door handle on the passenger side. I can't remember how the two 12/70 saloons I once owned were configured. I always thought that this was to allow the polite driver to open the door from the kerbside for the passenger, who would then flick the offside handle down to allow the driver to enter.

Thanks Robin, its good to know that other cars are configured the same way as mine. After some thought I had come to the same conclusion about courtesy, and presumably on leaving the car, the driver would lock his door by flicking the catch before walking round and opening the door for his passenger and then locking it after she had got out. I also wondered whether it might have something to do with avoiding faffing around with keys while exposed to moving traffic on the driver's side.

Robert, a quick look through the 12/70 Car Record Sheets is revealing. Drophead chassis 15422 notes "Door locks changed over", saloon 15740 "Door lock fitted on right hand side in lieu of standard" and saloon 15759 "Lock on o/s door instead of n/s". The normal configuration for the 12/70 at least was certainly to have the lock on the near side. I really should get out more. Where's that anorak? What's that - you say I'm not allowed?