Imperial take very little account of the personal statement in general. They use your BMAT score to short list you for interview. And in the interview, they very loosely base their questions around your PS, but focus a fair bit on the "why medicine" "tell me about work exp" "how can you contribute to IC" side of things.
I wouldn't try to make things too academic (by academic, I mean science focused and am not including work experience as I deem that to be vocational). For Cambridge, you can write out an additional statement in the SAQ and Imperial aren't too focused academic topics for interview.
And the whole point of writing about extra-curriculars is not to state you do them, but to show what you've learned, gained and developed from them. The reason why medical schools like some ECAs is due to the fact that it shows you have a life otuside of academia and studies, and that you have a potential outlet for stress. They are just as important as the books when it comes to studying the course and medical practice.