Brett, David and Rory
I did sort of half -wonder if Bell was a "plant"; given Rory's info re "Van Schwieten" - whimsically, I might say the name is redolent of the TV series "Hannay". Seriously, it would have been relatively easy for the Transvaal Secret Service to infiltrate hastily recruited Colonial units. The question being whether it was worth the effort. I do recall reading of accounts where members of certain outfits were suspected of being spies. A rather different example of a colonial defecting to the enemy was that of "416 Tpr. E.J.Hay" of A Sqn., Protectorate Regt; who most seriously DID NOT qualify for his DofM clasp when he defected to the Boer lines on 21st March 1900 (he was then under arrest) and later co-operated with Eloff's men in the Police Fort (info from Colin Walker's Mafeking Siege Register).
Rule 303 would apply in such cases..
Regards
IL.