Hey Paul, I'm actually on a very similar boat to you. I'm also in Uni studying Computer Science and plan on saving up a few years after graduation before committing to aviation.
If you're going to get a 2:1 out of your degree I wouldn't bother getting GCSEs/A levels. I don't think an airline would care if you don't have GCSEs or A Levels when you have an actual degree, you would have proven yourself enough.
Also, most of the ATPL material is of GCSE level so I doubt you'll run into problems.