Just taking this sad situation from another angle: this boss is ultimately the one responsible for making your relative ill. He is quite happy to let bullying continue in his organisation. He is a coward and a prize sh1t and not worth working for. Your relative is much better off without him, and needs help and support to move on, get better, and then find a way to earn a living elsewhere.
As others have said, there is scant recognition of the impact of workplace bullying in the UK and in fact many organisations run on a culture of bullying. Many people in these organisations collude with and join in with the bullying because they fear becoming a target, because they are cowards and because they start to become bullies themselves.
Best of luck for a happier future to your relative.