Thanks for the information Neville.
That is correct Rob, HMS Powerful and HMS Terrible did not have 4.7" guns. As for their origin, according to Afloat and Ashore: The Royal Navy During the Boer War 1899-1902 by Peter Singlehurst:
"As the situation in South Africa deteriorated the Terrible was ordered to join Admiral Harris at the Cape. On 20th October 1899 eighty Royal Marines, one sick berth steward and eight stokers as stretcher bearers, joined the first Naval Brigade to be landed. This brigade was organised at Simonstown for the defence of Stromberg. The Boer advance into Natal was also causing concern and on the 25th October two 4.7 inch guns from the dockyard store were prepared by the crew for service ashore. These were put abroad HMS Powerful for the defence of Ladysmith"
And:
"Following the Boer advance towards Ladysmith the ship was ordered to Durban to land a brigade to help defend Ladysmith and after taking on board two 4.7 inch guns on the 26th, the Powerful sailed for Durban. On arrival Captain Lamberton, together with the two 4.7 inch guns, four 12 pdr guns and 275 officers and ratings were landed. After travelling by train the brigade just managed to get into Ladysmith before the Boers managed to cut the railway line."
Gary