About 200 people died from cancers related to this
However, in all such discussions, one needs to be aware of the strong interest of the British government to keep all things around it's nuclear weapons program secret. So maybe the public figures are fake.
In hard drives or networks, errors are tolerable below a certain threshold. It's a different story once unrecoverable errors start to occur (data loss, system crashes, perhaps errors getting caught by higher-level things like exceptions).
I'd expect DNA, cells and biological systems are probably similar. The error correcting mechanisms can probably handle some errors up to a threshold (which probably itself varies between individuals).
Source: Mahaffey, "Atomic Accidents: A History of Nuclear Meltdowns and Disasters"