Earlier quoted context omitted.
The same forces that drove Tories to the extreme right also spent decades dividing Labour between itself. The first-past-the-post electoral system has no defense against well-funded interests essentially buying all the candidates. One could wonder if the substandard electoral system exists purely because of this flaw (or feature for the few powerful).
France has a completely different political structure and electoral system, and yet we've broadly seen the same phenomenon of the right wing's center of gravity always moving righter (is that even a word ?) and the left wing digging and splintering its way into irrelevance. The difference being that the electoral system produced a centrist rather than a populist (but in both cases Macron and BoJo are a pure product o…
The dynamics are same prior to runoff because the plurality electoral system gives no representation to the majority that didn't vote for the winner (almost a given since there will be >2 candidates).
You'd need proportional representation and/or an electoral system like Borda,RCV,Star or instant runoff to significantly proof against spoiler mechanics that the wealthy can exploit.
Again, none of these measures guarantees against money corrupting electoral processes, just makes it more costly and unsure that any given corruptive effort pays off.