Yes. I resigned from the NIIC for many reasons but one was that they were quite unable to read the building regs or indeed their own membership rules. I registered my own work for a while which is within the Building Regs provided Building Control accept your qualifications. However. The government, not through the building regs so I don't know what the legalities are, requires the offer of a Warrentie backed insurance for your work. Have you spoken to anybody about this?
In the main I am now finding that the general public are asking for Part P registration before they will take you on. I suppose its realistic since they know that your work is checked by an independant authority and that you are not a cowboy. That is not to suggest that you or I are cowboys but they do exist! I've seen their work.
PS NIC demand that you use their registration process and buy their warrantee at £1.50. Elecsa to whom I now belong provide instructions on offering the insurance and require proof that you are doing so, which is quite easy. They offer such insurance at 10% but of course nobody takes it up.