Call centres were also discovered using aggressive techniques to cold call potential donors after charities pooled addresses and phone numbers without permission.

Classes taught to civilians largely focus on the self-defence aspect of the sport rather than the aggressive techniques used by security professionals.

But in recent years there has been a shift towards more aggressive techniques and disrespectful attitudes.

But many have switched instead to issuing tickets for any amount they like and using aggressive techniques to get drivers to pay.

Companies that employ overly aggressive techniques can get their client websites banned from the search results.