There is GCSE-level (age 16 exams for the UK) maths and science, one tiny bit of more advanced maths. It should all be covered in the training, very few people have problems with this.
Like the others I would not waste the money at Oxford. If you really want to monitor computers at 35,000 feet for a bunch of rowdy drunks (the passengers, not Monarch ops, although in my experience that might also be the case) then use the money you save at CTC or similar; if you want to do some real flying instead an integrated course will not equip you well.
Do a modular course, do it at a school that only does modular so you are not given low priority. I would suggest Bournemouth if only because it is easy to get to from Ireland. Stapleford isn't bad for that either, or Exeter if there is still training there, but Oxford has to be a right pain.