Thing is the client wont know. An NVQ3 taking 3 years or a 2382 taking 2 Days will both give you a C&G cert, the client wont know the value of them. The only sure way would be NICEIC AC as the requirement is higher.
My first boss was an NICEIC Approved contractor and he didn't think you could have a 3 phase TT system.
Obviously not all are this dense but just putting it out there.