Let me tell you from experience. Getting in as a pilot in the RAF is VERY difficult. Your grades need to be very high and you need to have a history of showing interest in extra curricular activities, such as; attending cadets, voluntary community service, or having The Duke of Edinburgh's Award is a very good idea.
On top of that you need to show that your a leader. As an officer in the RAF you'll be leading other men and setting examples. Even if you have all this you still might no be what they're looking for.
But if at first you dont succeed, try again, they like persistence