At my school they dislike over predicting. They may give you a predicted grade sometimes if you ask for it, but they often make sure that all of your options aren't reliant on this. We did exams in the summer using the AS papers that people who were actually doing the AS levels sat, and from this we were given our predicted grades. The policy is that if you are within 5 ums of the next upper grade boundary then they allow you to have that predicted grade, but sometimes if you have done well all year and just slipped up they will predict higher anyway. Many teachers at my school are against overpredicting because on results day when people don't get the grades, they are disappointed. More so than if they couldn't apply in the first place, as they are just lying to themselves.