Even if killing cats for any reason, either deliberately or accidentally, is legal in the UK there are still two potential problems with starting the train: Terrible PR when the story gets out and opening your company up to potential civil litigation from the cat’s human as well as anyone else traumatised actually witnessing or contractually obliged to participate in (e.g. Driver) said death of cat. In summary, your brand takes a hit and you may lose money. As an added bonus a late train is less newsworthy in the UK than a funny cat so by delaying the train you might even generate good PR at no cost.