Jacobin,
I'm sure there must be an account somewhere of Methuen's travails that day. I will see if I can find a report in the papers.
I cannot see any biography or autobiography of the 3rd Baron. Does anyone know of one?
There was a recent book which may help? Stephen M. Miller (1999). Lord Methuen and the British Army. Routledge. ISBN 0-7146-4904-X.