Wikipedia: “A single point of failure is a part of a system that, if it fails, will stop the entire system from working”. Right. You try to avoid this in any decent system, building in redundancy at every critical point. The classic example is a chain, where any single link is a single point of failure. You can build in redundancy by, e.g., adding a second chain. So long as each chain on its own can support the weight, nothing bad will happen if one chain breaks (bad luck if both break, though).
Something like that principle of redundancy was meant to be part of the life insurance Part VII regime. You have the PRA which approves the default model of the insurer. The FCA is meant to look at the same thing from the point of view of the policyholder (the PRA being a prudential regulator, as I pointed out to the court here, see page 5). The Independent Expert provides further assurance with his/her ‘independent’ report. Finally, the court itself forms a judgment.
However, that principle seems to have been disastrously weakened in the light of the recent judgment by Justice Zacaroli.