The words in the link "...unsigned and unverified document..." suggest that there isn't as yet much solid evidence. But all schools have to be inspected regularly, and having myself suffered Ofsted Inspections, there isn't much that gets past their scrutiny. They interview parents, staff, community members, ancillary workers, pupils, managers, the lot. If they're any good at all, they'll spot any anomalies in the school's systems.