I do find this situation greatly annoying, when I renovated a house last year the plumbing and cable running I did myself was perfect, it was a work of art, tacked perfectly in place, every hole bang in the centre of a joist, spaced exactly according to building regs and the stuff the plumber and electrician did was a rushed mess! Do you have a certificate for the half of the house and the consumer unit that is already wired? If so and your competent then do you need one for the other half? Can you get an electrical safety test, bit like a yearly gas Safe certificate? The plumber doesn't insist on only signing off pipes he's installed himself!