"There is also a common law offence of outraging public decency, which makes it an offence to do in public any act of a lewd, obscene or disgusting nature which outrages public decency." 

Quoted from government response to nudity e-petition, 2008 Jan.

This ought not to be applicable to naturism. But in 2012 it appears that it might be the next weapon. On 2012-11-07 Stephen Gough was charged with Outraging Public Decency and remanded in custody until 2012-11-21. The charges started with the Sexual Offences Act, then changed to Public Order Act and only then to Outraging Public Decency. Later this case was "discontinued".

ASBOs (anti-social behaviour orders) have been made against naturists.

In 2012 a white paper "Putting Victims First" proposes giving the police powers that are even more arbitrary and undefined than POA s5:

3.30 Following the consultation we propose introducing a new flexible police power which combines the most effective elements of the various current dispersal powers into a single, less bureaucratic power. This would enable police officers or Police Community Support Officers (PCSOs) to require a person who has committed, or is likely to commit, anti-social behaviour to leave a specified area and not return for up to 48 hours. There would be no need to designate an area in advance. The power could operate in any public place, and in common areas of private land with the landowner's consent. This means the police could quickly deal with emerging troublespots, providing immediate relief to victims.