According to Karau and Turner's book, a Mrs Harold Gale reported that "Around 1900, the loco did a 'bunk'. It left Cholsey station without its coaches. Harold and Len Gale, returning from football in Reading, had uncoupled the loco while it waited in the bay platform." I can believe that Harold and Len told this story, but not that they actually did it. Surely the crew would have been in big trouble if they failed to notice, let alone do a brake test, before departing?
The Abingdon branch-line train was also known as "the Bunk". Local opinion is that this had something to do with the bunker of the usual tank locomotives. I don't think I believe that either, given that pretty well every GWR branch used tank engines. I wonder if the Abingdon name was copied from Wallingford?
I'd be enthralled if forum member(s) can elucidate / confirm / refute any of the above.
Really no worthwhile thoughts re "Bunk": have to wonder, maybe just "local poet gets inspired" -- perhaps while musing vaguely on tank loco's coal-bunker -- and his random whimsy happens to catch on in the area.
However, something perhaps slightly parallel: and again -- to my knowledge "as far as" -- in general Great Western territory (maybe further afield in Britain too?). The Marlow branch train was locally known as the "Marlow Donkey"; that on the Kemble -- Tetbury branch, likewise the "Tetbury Donkey". Possibility -- poetic conceits and figures of speech -- equating of flesh-and-blood donkeys (lovable and reliable, but slow and sometimes cantankerous "I'll do it my way" beasts of burden), with branch-line locos / trains? Also: in days when steam traction was the norm, a "donkey engine" was a widespread term for a small -- possibly stationary / portable -- steam engine, for small-scale power application. Sometimes, I understand, expression employed to refer to very small and light actual steam rail locomotives. Transferable up-scale perhaps, in a metaphorical way, to more-substantial but still small and light, "real-railway" locos?
And maybe adding a little bit into the general mix -- a much-loved folk motif, usually told about the lightest and most flimsy of narrow-gauge lines or steam tramways. The train, or steam tram, is waiting at a roadside halt; a local farmer shows up, road-travelling and donkey-(flesh-and-blood-kind)-powered. Train crew ask, "hey, Fred, aren't you travelling with us today? Is there anything wrong?" Fred replies, "No -- it's just that I'm in a hurry today; I can't be bothered with you lot". His donkey will get him into town, sooner than the train would.