Why have the UK Lib Dems won a by-election while gripped by a leadership challenge, disarray and infighting?
Easy really, a substantial majority of Brits take not a blind bit of notice of issues, policies or anything else when deciding how to vote:
The working class vote Labour, giving Labour dominance north of the Severn/Trent line and in inner cities everywhere.
The suburban and rural middle class votes Tory, enabling the Tories to win most seats in the South-East outside inner cities.
So, how do Tories in Liverpool or Labour supporters in Winchester vote? Lib Dem - hence their resilience. Ironically, exactly the same factors make it awkward for them to come up with coherent policies when they are an alliance of people as different as socially conservative Northern businessmen and southern polytechnic lecturers.