Is it 'shoo-in' or 'shoe-in'?

[BelfastBloke]

Quick question:
Is somebody a 'shoo-in' or a 'shoe-in' (to be the next manager of Man Utd, say)?

shoe-in.

I thought shoo-in but have recently been discovering on mumsnet most things I think I know like that I actually don't

Have found this though which backs me up.

bother.
don't let my DH know I'm not always right!!

here we are:

"Shoo in" was originally a racetrack term, and was (and still is) applied to a horse expected to easily win a race, and, by extension, to any contestant expected to win an easy victory. According to the Oxford English Dictionary, the first use of the term in print dates back to 1928, and the original sense of the term was not as innocent as you'd think. A "shoo in" was originally a horse that was expected to win a race, not by virtue of its speed or endurance, but because the race was fixed. The sardonic "subtext" of the original usage, now lost, was that the designated horse would win even if it were so lackadaisical in its performance that it simply wandered somehow up to the finish line and had to be "shooed in" to victory.