They are legal, but it is recommended you provide a warning to prevent being sued.The law states that you have a duty of care to protect people on your premises, including trespassers such as thieves. However, it also states that you are not liable if you’ve warned people a hazard exists. Therefore, we recommend you create a sign notifying someone of a hazard i.e. WARNING: These Premises Are Protected By An Anti-Intruder Device. Injury May Result From Unauthorised Access.
Primrose stocks warning signs for just 35p and we recommend you put one up. Such signs are a fantastic deterrent as thieves are largely opportunists and do not wish to put themselves in danger or tackle a property with an owner who takes security seriously.
In addition, the law states that you have a duty to innocent passersby and cannot add injurious toppings to perimeters lower than 2.4m. This includes barbed wire, razor wire, broken glass, nails and brackets, but not prickly shrubs, nor polypropylene fence tops. Our fence spikes will not cause injury, but cause such pain as to make it impossible to scale a wall.
Ultimately, while it may seem outrageous that you can be sued for trying to protect your property, the current legal framework protects against malicious security, while providing the right to protect your property.