Until the last couple of years, the only source for a plastic British colonial army was Esci. Esci released two boxes of British troops - the first was supposed to be for the Zulu war, while the second was a slight modification (including some Indian troops) to serve on the Northwest frontier. The first box was also reissued more recently by Italeri.
As the image below shows, the Ral Partha figures are substantially larger than their plastic brethren. The use of fairly thick bases allows the Esci soldiers to come up to a comparable height, but does not really create an illusion of similar size.
The Ral Partha figures, and the Esci troops on green bases were not painted by me - they came in a lot that I bought from Chuck Turnitsa. His blog is here: http://chuckgame.blogspot.com/