Best Material To Progress Cuckholding?

I remember seeing documentaries from the UK (maybe channel 4) on dogging, swingers, and a brothel. The dogging one was a bit grim but the swingers one looked like fun. The brothel was a series I think, made the business look very ordinary. So there must be at least one out there that looks at cuckolding or partner swapping.

I can't for the life of me remember any of the names of them, but I'm sure it was channel 4 or ITV or some other UK production company.