Your Personal Statement is increasingly becoming the deciding factor in UK university admissions. When universities hand out their offers they are doing it based on two pieces of information. Firstly, they calculate the probability that you will get your predicted grades. They must make this calculation because underfilling their courses will lose money for the university and overshooting their estimation will lead to crowded classes and a lack of resources per student.
The second piece of information universities have at hand is your Personal Statement. The statement that they read will not change and gives them something human in your application to relate to. universities not only want you to excel in the course you have chosen, they want you to contribute to the university at large. The more well rounded you are the more they will believe that you have something great to bring to the overall university experience.
An applicant who has an empty life, brings no contribution to their school, social circle or even their own self will struggle to get the place they want. Getting A and A* grades in isolation is meaningless as you can be sure the next applicant has similar grades but fills their extracurricular time with meaningful activities. A well written and clear Personal Statement can therefore push you to the top of the pile, giving you a vital edge over the competition.