Here you will find updated, official, guidance from the College of Policing on the way the Police should handle public nudity. This guidance has been given to all call handlers and front line police officers. It is very clear that ordinary naturism should not attract undue police attention but, if you are the subject of a call to the police and you are just enjoying the sunshine and neither the call handler or police officer has read the document it would be very useful to download a copy yourself and keep it with you.
If you click the picture below, you can see and print off the entire document
This guidance is very good news for anyone who enjoys their own garden or the open countryside as nature intended but does rely upon some degree of common sense, so going for your naked picnic a metre away from a clothed family is very likely be seen as outside of these guidelines.