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 of their respective countries' establishment).
I don't think different systems differ so much as far as being rigged goes, it's just the rigging that changes. In the end, power is always in the process of cooptation.
France is essentially first-past-the-post with a single runoff for presidential (who is a very powerful executive like US model + he can dissolve parliament).
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.
Also BoJo is no centrist. He's spearheaded Brexit (some allege his buddies made bank by arbitraging currency futures pre/post vote), and he's been coordinating with Farage for a long time.
The right wing moving righter? Hardly. It’s easy to see that politics has shifted drastically left. Political stances considered mainstream 30 years ago would end careers today. The so called “extreme right” Tory government, before the last reshuffle, had 3 of the 4 top government posts occupied by MPs from minority ethnicities. What you consider to be ‘moving righter’ is in fact just louder complaining due to the accelerating movement towards the left.
I think you're focusing on racism to the exclusion of all else.
Britain has sold off vast swathes of housing stock and is privatising ever more healthcare delivery. Zero-hour contracts are a thing nowadays. Industries that most countries run as a public service have been privatised.
Collectivism has been replaced with neoliberalism. Our country has swung miles to the right both socially and fiscally. But yes, you can be out and brown.
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).