You will find police officers strolling around the site, usually in the main field. All of them are very approachable and will welcome a chat. Cropredy is a favourite for them, there's very little crime, and their duties usually comprise escorting lost children to a meeting point or helping the inebriated to find their tent (or a stomach pump). At the end of the evening, they direct the surging crowd as they exit the field. If your preferred choice of relaxant involves herbs that do not meet the standards of the Good Housekeeping Institute, keep it to yourself, don't approach a copper with a joint in your hand, don't try to deal (especially not to police officers) and I daresay all will be well. In other words, don't be silly. If you deal in anything that could be considered a "hard" drug, you'll be shopped in an instant. Cropredy has an excellent crime-free record, and the returning folks want to keep it that way.
There are many tales of the police at Cropredy, but two should give you the flavour... A uniformed copper strolls past, his helmet replaced by a jesters' cap. Someone cries "Like the hat!" Copper stops, leans over and says "Shhh... I'm working undercover..." (Thanks, Colin!)
On another occasion, as the crowd were leaving the main field, three police officers, standing in line, were directing the flow of bodies. Each had a cardboard strip over the badges on their helmet. Each strip had "Hello" written on it. And they posed together for many photographs...
If you need the cops, they can be found at the top of the main field. In order to police 20,000 festival goers, less than 30 officers are allocated. That should tell you something about the conduct of Cropredy. Crime is rare, and in the eighteen years I have been going to the festival, there have only been two serious injuries that required removal to hospital. One fool tried to cook in his tent, and set it on fire. Another person slipped over and broke his neck, but he lived. Indeed, the last time I heard of him, he was making excellent progress. Not bad for eighteen years...