UK Private Investigators & Workers On Sick Leave - Employer Use Of PIs

Looking for case studies / people to interview for a story on PIs. I am a journalist at a major UK newspaper and am looking into the use of private investigators by employers. I am hearing that most PIs spend a lot of their time investigating people working from home or on long term sickness leave. If you are a PI and have stories, or know of someone who was busted by PIs while on sick leave / wfh, I'd love to hear from you.