JIB Gas Service Engineer (Gold and Blue) Card firstly is intended for fully qualified operatives with advanced gas fitting skills. Moreover certifies that they have had the extensive technical and health and safety training necessary to work without supervision.
There are two additional qualifications that you will want to ensure you obtain at the end of any training course for gas engineering: Gas Safe registered and your ACS in Gas. In addition without these two certifications. You will not be able to work legally as a gas engineer, no matter how much training you may have.