First of all there is no such general offence as 'indecent exposure'.
There is an offence of 'Exposure' but the name is misleading. It is actually 'Aggressive Exposure'. It was very carefully worded so that it could not be applied to naturists. The important point is that there must be intent to cause fear, alarm or
distress. The defining judgment states that 'outraging is a very strong word' and that the behaviour must go well beyond merely offensive. The offence must be in a public place but the definition of public place is rather technical.
There are no specific prohibitions of nudity. The Victorian statutes have all been repealed. Also the enabling power for councils to make bye laws regulating the decency of swim suits has been repealed to ... protect naturists
from busy body ... councillors.
Public Order legislation is sometimes used against naturists. The old favourite of police and authorities when they want to make up the law as they go along is section 5 of the Public Order Act 1986. But when the victim refuses to be bullied, the
prosecution finds it difficult to obtain convictions.
Another police favourite is to drag up the ludicrously old law, the 1824 Vagrancy Act, which makes it illegal to expose the male person.