Contrary to popular belief, simply being naked in public is not illegal in England & Wales.
British Naturism has up-to date guides on the legal situation here
The latest College of Policing guidance on Naturism is available here.
In summary:
"In the lawful situation where there is an absence of any sexual context in relation to nudity and where the person
does not intend the behaviour to be, and is not aware that it may be disorderly, it will not be appropriate to take
any police action."
Anyone undertaking naturism in a public setting should familiarise themselves with this information and take copies (especially the College of Policing guidance) with them.
The rights of naturists is now recognised by many organisations including Forestry England