I have found that on the internet.
In February of 1889, a cooling chamber was installed on the RMS Grantully Castle, and in Cape, about fifteen tons of grapes were loaded into this chamber. But, for couple of reasons this shipment did not arrive in London in good conditions. The temperatures were kept too cold for fruits, and the wrong kinds of grapes were chosen for shipments.
So I guess that the methods of transport improved by 1940.
Unfortunately, I cannot find any information about wartime food shipping from South Africa. I guess that Portugal is the only other option, with harvest of wine grapes during September.