OAT do not reject candidates who are otherwise suitable for the APP on the grounds of maths/physics performance at selection. They take the view that if you are assessed as having sufficient pilot aptitude, motivation, and maturity, then you will be able to get up to speed by doing a course of pre-ATPL Maths and Physics private study. Contact Mike Taylor, OAT's Career Development Officer though the OAT website for more information and he will give you personal advice.
OAT also provide a one-week pre-ATPL Maths and Physics refresher, but if you were good at these things once, you probably won't need that. A bit of self-study should sort you out.