Have you tried Googling "adult payment processor uk"?

Connecting 'adult' with any name drop would probably lead to, "Off with his head' (TOS and short leash.), but just think big. The top US processors have UK presence.

You mention "making a site". It had better be money making ready because the processors for 'adult', sometimes pretty loosely interpreted, rake in steep fees. I understand 'higher risk', but ouch.

I do not have any sites that fall in this class, but built a local/regional site for 'people who wanted to meet people', and learned a lot. The owner had to practically personally guarantee his first born; the cost was outrageous. It's a 'marked' market so an excuse to charge big.

Not my area - maybe the risks remain truly high enough that that fees are indeed fair, but ouch.

BTW - Watch your step. It was my opinion at the time (about three years ago) that a lot of the processors that will take this business are the most unsavory link in the chain.

On a now defunct UK board there were several discussions on this topic a few years back. One problem is processors moving the goal posts. They may see your site selling, say, provocative lingerie as a ligit clothing site when you register but down the line they decide that maybe it is "adult" content after all and zap your account at zero notice.