I'd agree that you need to be sure what you're looking for. British society is probably not quite like US society but I think there are similarities ... I found true love via the internet, myself, when I had decided that it wasn't just a "sexual friendship" but a fully configured relationship that I was after. We've been together now for fourteen years, so it's worked well for us. I met him when I was 48 and although I had lots and lots of friends via social settings I wasn't meeting unattached men who wanted a relationship.
So I set about a campaign, via the dating site I was using (and I think there are many better sites out there now), and made a point of meeting a range of potential partners for real rather than spending ages merely on line. I looked after my own personal safety by always meeting in a public place, always telling a close friend as much detail as I could about my "dates" and where we were going and so on. I met a lot of unsuitable people (by which I mean people with whom I had little or nothing in common and with whom there wasn't the faintest suggestion of attraction) before the right one turned up, and the trick for me was to treat it like an informal interview (sorry, Will!).
It worked for us. Some people find a personal ad in a paper or magazine works. Some find their true love via Mudcat or other internet forums. Some get lucky in their own neighbourhood in interest groups. Some get introduced to friends of friends. There's no one way. If all you want is a sexual friendship you'll find that fairly easily on line. There are a lot of people out there looking for uncommitted sex, including a lot of married people (as I discovered, despite specifying I wanted to meet unattached men).
Good luck with the search, whichever way you choose to set about it!