> The County Adit in central Cornwall is probably
> the longest mining related tunnel, at 30 mile
> with its various branches. The recently constructed
> water "ring main" around London is probably the
> longest otherwise.
If non-mining tunnels and their branches are allowed, the underground
part of the London Underground must be in with a chance.
Also the Channel Tunnel, which I believe is three parallel tunnels,
each at least twenty two miles long. Even if the tunnel is British
for only half its length, you've got at least thirty three miles.
Stephen Benham
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