To add to what's been said above, the GCSE English/Maths grade C requirement isn't specific to Russell Group unis. I currently work at a post-92 uni which won't consider candidates for any degree courses without those GCSE grades. Proof of a basic level of literacy and numeracy are mandatory for all applicants. You may be able to shop around for unis which accept a lower Maths grade for your chosen degree, but you're limiting your choices - and there is the possibility that you may not find one.
Many colleges won't let you enrol on an Access course without those GCSE grades, for that reason. There's no point you doing a qualification which is only used for uni entry, if your other qualifications mean that you'd be unlikely to get into uni anyway. It may be that your college will only permit you to enrol part-time, as they expect you to retake the GCSE Maths alongside the Access course.