Kenya and Tanganyika may share a border but they are not the same. The OP makes the point that the British had recently taken over the latter, which had been German East Africa, and also that the aeroplane concerned flew there. The Francombe memory may be fallible, but I think he would not mis-remember flying but could well have the type number of the aeroplane wrong.
As Megan posted, the DH51 was shipped to East Africa not flown.