This is one of the most successful U.K. based sites. It covers dating and making friends; it is extremely user friendly, and easy to navigate. At the end of April 2005 it had 624 new members that week, it also records clearly on the home page the amount of people logged in at any one time. It offers a free tour, which you have to log in to access.
It offers a very clear view of their terms and conditions, which also includes common sense suggestions if you are new to the on line dating scene. Definitely a place to start if you are trying to find a partner in the U.K.