STD checks are easy. Find your local clinics and get one yourself. This will give you a starting point. If the models are from your area, insist they go to the clinic or have their own certificates. A monthly check is a minimum.
Getting models is a tough one for me to answer. Try searching for agencies in the UK. I'm sure there's something online, so try Google with the terms that a model would use.
Google That will start you off.
Also, get a site going so people can see you're serious. Agents are wary of people with nothing to show to prove they're real.
If you just want to get laid. Get a hooker, lot less trouble.