http://www.gardenlaw.co.uk/walls.html

Protecting against Trespassers

Traditionally owners have put deterrents to trespassers on their wall or
fence and if it is a party wall just on their side. You will often have
seen spikes or broken glass or barbed wire on the top of walls.

However, if the wall/fence borders the public highway, then the local
authority has powers to protect the public by having the deterrent
removed if it thinks it could cause a danger to highway users. If the
deterrents causes a nuisance or by your negligence injures a passer by,
then they may be able to sue you. Err on the side of caution because if
the deterrent is considered to be excessive you could open yourself up
to a criminal prosecution for an injury caused.



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