Without any sharp implements the cops will just tell you to piss off, or you might spend a few hours in a cell and get released at 3am. If you're carrying a knife though and don't have a really good reason for it then it turns in to a crime that carries jail time. Knives are a big problem in the UK.Why would you spend all that effort to get on the roof but not bring something to cut it down with??
So what happened with Season 5? Did they find it so quick that no one bothered to tell us about it?