Motorcycle Safety & Driveability: U.K. law regarding motorcycle alarms, motorcycle alarms, legal situation

Question
Hi Mr Booth
I have heard that it is illegal to have fitted, an alarm / immobaliser that cuts the ignition out whilst the engine is running on a motorcycle, and that the alarm / imobaliser's only purpose is to disable the start function and, or, sound an alarm.
Please can you tell me if there is any truth in this?

Answer
Hello Allan.
This is an interesting one!
I can't imagine that such an alarm would be illegal, could you tell me where you got your information? If such an alarm were illegal then what would be the legal situation over the kill switch on the handlebar? That would do the same thing.
Yes, immobilisers are designed to prevent the engine being started in the first place but I can't see how an immobilser cutting out a running engine would be illegal. Apart from some obscure ruling where if a thief were to be injured as a result and thus having grounds to sue for personal injury, I can't think of any law which would prevent such an alarm being fitted.
I'll try to investigate this further and update you. Please can you let me know where you heard this rumour and any other info you have on this?
I'll be back in touch as soon as I can.
Andrew.