UK university - Clearing?

No I don't think it will diminish your chances at all. For starters through Clearing you get a better chance of talking to an actual person, rather than them just judging you on your application, as you apply first to the uni itself, and then if you get accepted you apply formally through UCAS. So they will judge you firstly on your grades and the subjects you've already studied, and then way after that they will see your application. Also a personal statement is there for a few reasons, not just to talk about why you like that course but also to give an idea of your english and grammar skills etc, your personality and to show that you have a life and other interests so are a well-rounded person. And also remember that they deal with clearing every year, so they will know how hard it is for students to get onto popular courses and are more willing to bend their usual rules to fill their course, so will be favourable towards people with lower grades or who intended to go for something different.