(see also his Blue Patrol tunic and Full dress tunic)
The mess dress uniform was a necessary part of all British and Commonwealth services kit, especially prior to WWII when formal dinner occasions were very common. Mess dress is still worn today but is often rented, not owned if the owner doesn't attend formal events often. Usually the outfit combines a short waisted dinner jacket, a waistcoat (or vest) and trousers or more high-waisted pants called overalls. Usually shirts and ties were private purchase formal wear. The outfit would come in both service color for winter wear and white for summer wear. Piping, arm details, color and insignia was unique to the service branch.
As part of the dress, the Lt. Col. wears a pair of metal and enamel wings on his lapel and a pair of gilt branch of service crest devices on both lapels. The buttons are SAAF eagles and crowns. The rank appears on the shoulders.
Lt. Col. Pope would have worn this uniform with a (probably) dark blue waistcoat and black tie for black tie occasions. In this case he is wearing a white waistcoat and white tie for a white tie occasion. These rules of dress would have been called out in his invitation. I have not seen this outfit photographed nor have I seen printed regulations which would be very interesting to confirm details.
A close view of the gilt and enamel mess dress wings that came with the uniform. They are relatively small and are die struck out of metal as opposed to the larger service dress wings constructed of bullion fabric (see Pope's blue patrol uniform). These are not sweetheart wings although they are very similar in size.
A close view of the matching SAAF insignia devices. These are really interesting as the initials on the crest are SAAF-ZALM. This Afrikaans designation, Zuid Afrikaanse Lug Mag, was in use only during 1922-1926.,After 1926, the initials were changed to SAAF-SALM, or Suid Afrikaanse Lug Mag. Therefore Lt. Col. Pope must have purchased this uniform very early on and continued to wear it during his career. Upgrading rank as he went.
A nice close view of the Mess Dress cuff detail. I have not idea how this relates to the SAAF or any of its history. But very nice tailoring!
The rank is that of Lt. Colonel with one crown and one pip. Given the age of the mess dress. I imagine that the Lt. Col. had been wearing this uniform since he was a Lieutenant.