Should I sit an IELT?Watch
The IELTS exam is designed for non-native English speakers, usually to gain entry to university or for visa purposes, to help them prove they have a good enough level of English to work or study in the UK.
If you want to prove your level of English for employment purposes, you could look into doing a functional skills level 2, which is equivalent to GCSE English and is designed for adults who didn't pass GCSE but want an English qualification. These courses are run for free by local councils, so if you do an online search for adult education in your area, you should be able to find the local service that offers these.
If you need the GCSEs to get access to university, then you'd need to do the GCSE as most universities won't accept functional skills. And universities won't ask for or accept IELTS because you're British. Some universities can be flexible with their entry requirements and could give you a place on a course with lower grades if you're an otherwise good candidate, for example if you have lots of relevant experience. The best way to find this out is to call the university you're interested in directly and ask them.
Hope this helps, best of luck - Mark