A slight divergence (apologies Alan) to answer Peg Leg's Question. It was many years ago now (rather depressing to be able to say that) but, I did my BA and MA dissertations on the military aspects of the 2nd Boer War (although I no longer have the copies of the records from the inquiry I took from the National Archives). If you want a plausible reason for vehicle development, you can make it an outcome of the post-war Iraq style inquiry (a far more effective one I might add).
2 potentially viable reasons:-
1) French's destruction of the Cavalry (in terms of exhausting the horses) to relieve sieges meant the Boer Commandos were able to escape (with the gold reserves of the Transvaal Republic) so motor vehicles might (emphasis on might, as fuel would potentially limit it), alleviate the problem in the future.
2) Concentration camps apart (although the Liberal government was able to make some headway in the next election with moral outrage overage them), from a purely military standpoint, Kitchener threw huge amounts of resources and hundreds of thousands of troops into a vast, semi-fortified telegraph network to detect Boer Commando movements. You could make the case that with motor vehicles, this would be unnecessary in future.
To return to the story. Does the development of the Valiant and it's successor totally butterfly the Churchill? Also, is the use of the Lion in tanks having any appreciable effect on aero engine development? Perhaps getting Napper to tool up earlier rather than have to get a kick in the proverbial posterior from English Electric?