Personal statement lieWatch
If you honestly believe that a 6th form/college/uni won't do a background check- don't even bother in the first place. Trust me, you do not want the embarrassment of being confronted with your own lie in your interview. If it doesn't happen then, then soon enough...the truth will come to light.
All dramatics aside though, be confident in yourself and your capabilities. To lie in your personal statement isn't the best thing to do. It's the first thing that the admission board/tutors will see. It just suggests to me that you are insecure and are looking for ways to validate yourself (which is probably the polar opposite impression you are trying to give).
Bottom line is, no matter what happens in life, stick by a moral ground (i.e don't cheat,lie,steal etc). It's more valuable to be a morally upright person rather than just have loads of accolades.
I really want to say I got a gold certificate in UKMT senior challenge, If im not being interviwed surely I could get away with it.
If you really want to lie, then you're not the sort of person that universities, or employers, want.