With so many digital cameras around, I'm surprised that many of these type of images are still seen in processing labs.
Basically, if anyone in the photos is under 16 (in all circumstances) or under 18 (in certain circumstances), even simple nudity might be regarded as a breach of the Sexual Offences Act 2003. (After some questionable arrests in the past, the police and the Crown Prosecution Service have at last come to recognise that there's nothing wrong with, for example, parents taking innocent pictures of their kids in the bath. However, many processing labs tend to exercise caution regarding any photographs involving child nudity).
As long as the people in the pictures are over 18 years old, it's basically 'anything goes' as far as the law is concerned. It's illegal to publish or distribute material which is likely to deprave or corrupt those who might see it. However (even when publication or distribution is concerned), it's a defence to show that the only people who were likely to see the images could not become depraved or corrupt because they must already be depraved or corrupt to want to view the images!).
It's the (extremely remote) possibility that a lab might be deemed to be 'distributing' photographs when they return them to the photographer which makes some labs wary of doing so. However, simple possession of pornographic images (other than those involving minors) is not an offence. It doesn't matter whether the images show men, women, sheep, goats or whatever. Neither does it matter whether the practices depicted are 'normal', 'kinky' or almost physically impossible. Anyone can possess such images without fear of prosecution.
Chris
(PS: When I was in my teens, my mother worked at a photo lab. During peak times, she would bring many thousands of photographs home, in order that she could check the quality of the processing. Going through them to look for all the '