So …
The United Kingdom is made up of England, Scotland, Wales and Northern Ireland. Britain is a big island made up of England, Scotland and Wales. Scotland, Wales and Northern Ireland have devolved governments, which means they take care of themselves up to a point, then the U.K. government takes over; England has no separate government, just the U.K. one.
Policing is one of the devolved powers, though generally the laws they police are the same. Nudity is legal in U.K. law, but is not always socially acceptable. (A good analogy is that there is no law saying we have to form an orderly queue, but it is socially unacceptable to jump the queue, and is still liable to incur the death penalty from an outraged mob).
Police forces in England and (I think) Wales are organised broadly by county; how strictly or otherwise they enforce or interpret any particular law can vary from county to county, depending on individual officers. Scotland and Northern Ireland have separate police forces, which again operate according to their own preferences and prejudices which can reflect the national mindset as much as the strict law.
Steven Gough managed to walk naked through England from Land’s End to the Scottish border with very few problems, but then got repeatedly locked up in Scotland because the Scots applied different rules to nakedness; I understand things are lot freer up there these days. Ireland is generally a bit uptight about bodies and nakedness so nudity, public or otherwise, seems less common there. Don’t hear much from Wales, but it has lots of remote countryside where police never go.
A park area outside Nottingham (England) known as Sherwood Forest (yes, robin hood’s old stomping ground) has become a free range naturist haven, largely through the efforts of a hardy few standing for their rights and working with the local authorities; there are even official notices up saying that public nudity is legal, naturists will be seen, get over it! There are plenty of locals who are now used to naked people (nearly all men) walking the area, but now and then there’s a Mr Angry or two who make a fuss, but get told by the police to stop shouting.
The recent spell of good weather has produced a flurry of articles in local newspapers/websites explaining that it’s perfectly legal to be naked in your garden, and elsewhere - there seems to be a pro-naturist faction at these newspapers’ head office who makes sure the correct line is put out. However, these articles always carry the caveat from the local police that people should be careful about not upsetting the neighbours, which one can interpret as the police discouraging people from getting naked so they don’t get irate calls from neighbours that police officers then have to deal with; police everywhere hate to be caught in the middle of neighbour disputes, and trying to convince someone who “knows” that indecent exposure is illegal that being naked is not illegal is not why they joined the force.
Hope that helps, JBee