Universities have rigorous verification systems. If a student is found to have gained entry using fraudulent documents, they are typically expelled immediately, and any credits earned are voided.
Most employers verify qualifications during the background check process or at any point during your employment. Discovery of a fake certificate is grounds for immediate dismissal and can lead to being blacklisted in your industry.
If you need a qualification quickly for employment, "Functional Skills" Level 2 is often accepted as an equivalent to a GCSE Grade 4 (C) in English or Maths and can sometimes be completed faster.