there is a precedent of sorts with when Alec Douglas Home became Prime Minister
At least Douglas-Home had the decency to wait until the incumbent died before contesting the seat, though the initial candidate – George Younger – was withdrawn, allowing him to stand.
Private Eye were incensed by the skullduggery and then-staffer Willie Rushton stood as an independent candidate with the slogan ‘Death to the Tories’, gaining 45 votes 
Anyway, the Makerfield by-election ain’t over till that fat lady sings, though it does appear that she’s rehearsing.