Re: a person with ncce after name has drawn up house plans>
In a self-build situation, the lender will ask to see the P.I. insurance of the architect or engineer who is supervising the build and\or making periodic inspections and issuing certificates. This may or not be one and the same as the person who drew up the plans.
By the sound of things, this NCCE-qualified person (what does this mean by the way? I am not familiar) only prepared house plans and does not have a further role in the building process. If you had intended to use this person to inspect the building work, fire him/her and hire someone else.
You need somebody to inspect the actual construction. This person must have P.I. insurance (if you are getting a mortgage and it is a self-build house - and even if not, it would be foolish to have the work inspected by someone who is not insured). While this person cannot certify that they have designed the house, they can inspect the plans and pass them, and they can issue a letter to the lender to confirm that the plans are up to standard. That should be all you need.
Your only serious problem would be if the NCCE person had carried out building inspections but was now not in a position to issue certificates to the lender. (OR of course, if you have already had building work done without any periodic inspections).