UCAS PlagiarismWatch this thread
I don't understand what you're asking. If you write it yourself, it's really rare that it gets flagged, from my understanding. It might be basic phrases such as "I was inspired by" that flag. Unless you've copied a whole paragraph, I've never heard of it happening.
What I'm trying to say is that any personal statement needs to be below 30% as that is what it says. The second thing that I said is that, isn't 30% of having similar things in your personal statement to another personal statement a lot to copy from?
Bear in mind that even going over the 30% doesn't automatically do anything, it's reviewed by UCAS who then determine whether to report it to the applicant's choices. The choices then have final say with what to do with that information.
The short answer is, unless you've plagiarised substantially, it's not going to be an issue.