Peaceful Man Arrested for Defending Himself. Stun Gun is a "Firearm", Self Defense is "Vigilantism"

Article

A taser is considered a "firearm" and defending yourself against violent attackers is considered "vigilantism".

From the article:

He had bought the stun gun, which was billed as a 'self defence torch', from a Dutch trucker after his friend was robbed by migrants whilst driving through Calais. 

The court heard the devices are legal in both Holland and France, where they are available freely at petrol stations and are frequently carried by lorry drivers. 

However it is classed as a firearm in the UK, meaning Mr Garrett was arrested on the spot when it was found in his vehicle. 

...

Sentencing Mr Garrett to six months in jail, suspended for two years, Judge David Goodin said he understood the trucker had been put in a "very difficult position" by the ongoing chaos at Calais. 

He said: "The court does accept international drivers coming from northern France through the Channel ports have a particularly difficult time of it presently because of the determined attentions of illicit immigrants who want to hitch on unobserved and get themselves to England at very nearly all costs. 

"One understands the more desperate they are the more alarming it is for a lorry driver who might find in the course of an inspection that he has such unwanted guests on his wagon. 

"Nevertheless the law cannot accept any attempt of vigilantism whatever the temptation may be for lorry drivers to arm themselves for the purpose of repelling these illegals." 

Wikipedia:
Persons alleged to be escaping the law or above the law are sometimes the victims of vigilantism. Vigilante behavior involves various degrees of violence. Vigilantes may assault targets verbally, physically, vandalize property, or even kill individuals.