Steve Firth wrote:

Yes, now explain the screw.

The electrician acting as expert in the coroner's court reported that
the screw and rack had shifted slightly over time: the report in the
Evening Standard reads thusly: "Evidence to the inquest from electrical
engineer David Latimer, who examined the kitchen, was that a screw from
the rack had caught the side of the electrical cable. Over the years the
rack and screw had moved slightly so that eventually the screw touched
the live wire in the cable."

The claim is thus that the screw had just (by less than a millimeter,
say) missed the live conductor when being installed, but (guessing) had
penetrated the sheath and nicked the inner insulation of the L
conductor; and the "slight movement" - maybe the rack sagging under load
making the screw tilt upwards slightly in response - had finally caused
the screw to make contact with the conductor.

The "shift over time" idea is needed to account for the rack having been
tingle-free for the initial 3 years? or so of fault-free operation - had
the circuit merely been turned off during the initial putting up of the
rack, the rack would've been live from the first time the circuit was
re-energised.

It's a plausible explanation of an implausible event; statistically,
even the implausible happens once in a while.

HTH - Stefek