I found this set of envelopes on Ebay, and I “had” to buy it.
It has South African stamps with OFFICIAL overprints on that I was still missing in my collection.
I guess I will put the envelopes as is in my album.
My policy is not to remove stamps from an envelope with significant labels, postmarks, and markings.

Folkestone is on the English Channel just to the south of Dover).
A postmark on the back from the Folkstone post office is dated Apr. 27, 1936.
The lettering at the top says ‘In Sy Majesteits Diens’ / ‘On His Majesty’s Service’.
‘His Majesty’ would be King Edward VIII, at the time king only since Jan. 1936. He would abdicate in December of that same year, to marry American divorcée Wallis Simpson. George VI then became the next king of England.

Minchinhampton is south of Gloucester in the Stroud District.
A postmark on the back indicating the arrival date shows Jul. 10, 1933.

It looks like it arrived on Jan. 11, 1932, so the letter must have been sent by airmail.

It looks like official stamps were offered for sale to collectors at the exhibition.
(Stamps with the ‘Official’ overprint are designated to be used by government departments and agencies for official correspondence.)

It was sent on Oct. 24, 1950 and just to Cape Town.
The customized registered mail postmark mentioning the exhibition is unusual.

It was sent on May 4, 1948. The 1947 stamp on the left features King George VI.
That uniform he is wearing looks like a navy uniform (he served in the Royal Navy as well as the Royal Air Force; was the first member of the British royal family to be certified as a fully qualified pilot).

I love this 1936 stamp that depicts the mine shaft machinery of a Johannesburg gold mine. Also on the stamp, the mine dump of excavated earth, and the skyscrapers of Johannesburg behind it.

The letter was sent to King’s College Hospital in London SE5 in August 1935. The hospital was established in 1909, and is a major teaching hospital and major trauma center today. It is referred to locally and by staff simply as “King’s” or abbreviated internally to “KCH”.

The coat of arms with the leopard on the rock and motto “Lux in Tenebris” (“Light in Darkness’) is that of Nyasaland— a British protectorate, later part of the Federation of Rhodesia and Nyasaland, and now the country of Malawi.