Hi business man,
Well you can try it on with building control and see what they say. It's important you really know what you're doing, especially with the testing, not just that you can convince building control. Download the model Electrical Installation Certifiacate forms for the 2011 amendment and ask yourself if you are confident you know exactly what to write, what boxes to tick and how to record all the test results. If not, then at the very least you still have a lot of reading to do

. Doing it this way, if BC will even let you, certainly wont save you any time, but maybe a little money.
Back when I did mine, I started off going the building control certification route, because back then the Part P doc said building controls had to cover all the inspection/testing from the initial building notice fee. But many, including mine, were just refusing or saying they couldn't do it. Mine wanted me to get the work done then get a spark in to do a PIR. They did an inspection of the first fix, and a regular inspector came round who clearly didn't really know what he was looking at. He glanced at a few wires, possibly seeing if they were routed in safe zones, but possibly just staring blankly. He didn't even want to go in the loft where most of the wiring was routed (it was a bungalow), then spent most of his visit frowning at a timber beam that had been put in when the previous owners had had an extension in the 70s and was precisely nothing to do with any work I was doing. All not very satisfactory. That situation and the fact I then had access to test equipment was what drove me to try on the other route which they fortunately accepted.
But nowadays, the guidance from central government, and the building regulations themselves, have changed a bit and allowed building controls to charge for inspection and testing, and generally clarified things a bit I think. So building controls have I think got their **** in order a bit more and have set up ways to get testing and inspection done properly and have a schedule of fees and all that. So probably best to get them to advise. For me I lumped everything for the renovation that was notifiable on the one building notice (was also a window enlarging including new lintel etc etc) and it was something like 200 quid if I recall. You'll have some element for testing/inspection but it may be reasonable compared to the battle you might have to get them to accept you are competent to do it yourself and the cost of the test equipment and the time learning etc etc. Not sure how many inspections they will want - for me it was gonna be first fix and completion, but I 'took over' after the first inspection.
The first thing I did was asked my supplier to replace the old meter with a new digital one and at the same time please install an isolator so the consumer unit can be conveniently replaced in the future without having to pull the service fuse. At that time, and with N Power as my supplier, this was all done free of charge! I hope you have the same luck as me! My new consumer unit could fortunately go in a slighty different location to the old one so I could leave the old one in place but strip out the whole old installation down to one socket fed off the old CU so I had some power. I could then install the whole new installation, then at some point got N-power back to move the tails from the isolator from the old CU to the new one. Again I think it was free.
90A fuse sounds fine. I had a 60. I was gonna ask them to upgrade it when I was finished but it just wasn't necessary. Was only a 2 bed bungalow with a big electric dual oven, but no electric showers. Even if you have a bigger house and have electric showers, I cant see you ever popping a 90 A service fuse to be honest.
I honestly cant remember the total cost. It would have been the notification fee I mentioned then just the materials. I used a Hager CU which a lot of pros would still recommend with Hager components. Had a couple of RCBOs with the rest split across 2 RCDs. Included mains with battery backup smoke heat and CO alarms, etc. Got everything from TLC. Im sure it was well under a grand for all the materials.
EDIT: Didn't see the post above. Seriously don't pull your service fuse, even if it isn't sealed! Get your supplier to fit an isolator!