Being a member of a CPS, such as NICEIC or NAPIT, allows you to notify domestic work. The requirements for joining one of these schemes has been tightened up over the last year, you can check what you'd need from their websites. If you want to carry out notifiable work - rewiring, consumer units, etc - then this can be regarded as a cost effective means of doing so (that is all I get out of being a member of such a scheme).
Having a 'gold card' in my opinion is moderately irrelevant with respect to being able to work for yourself doing domestic work. I don't have a gold (or any other colour) card and never have, and have run my own successful company doing mostly domestic work for over 10 years now.