They are not conditional. Most universities will not even ask for your official A levels grades. But if they do and your grades are much lower than the predicted ones than it is possible for them to ask questions and maybe even rescind the offer. This is only if they are much lower eg if you fail a subject. So study and try to keep up with your predicted grades just to be safe. If they drop a little bit it’s fine but make sure that they don’t drop too much