They met for 30 seconds - she then stalked him for four years

The meeting between motivational speaker Brad Burton and Sam Wall lasted less than a minute. She posed for a picture with him after attending one of his workshops and later left a glowing video testimonial.

It was unremarkable, Mr Burton says. "Just one of the thousands of people I must have met over the years."

Two years later, she started attacking him online.

In hundreds of posts, Wall described him as manipulative, a psychopath and a sociopathic abuser. Day after day, she accused him of making death threats, breaking her windows and killing her cat - all false allegations.

"She put it on social media across all platforms. She was painting a picture that, somewhere along the way, I had done all these things and I was trying to cover it up," Mr Burton tells BBC Panorama.

"How do you prove a negative? That I had not poisoned the cat? Social media and the way it works, it's guilty until proven innocent."