I am building a extension and I am installing the electrics.
9 extra sockets, 3 light roses, and earth bonding.
Do I need to haves these checked, I am fully aware of electrics, but I am not reg.
You need to get on to building control at the local council and tell them you are doing the work, they will then send somebody out to check the work and certificate it, remember the 17th edition has just come into force, you say you know about electrics, well I hope you know enough for it to pass, whatever you do, don't start work before you have phoned them, they take it very seriously now, good luck, Ray
But since you are building an extension, you will of course already realised that the WHOLE STRUCTURE needed Building Control Approval anyway, and the Part P electrics is but one tiny aspect of the whole job. So, given that you presumably have BC involved already, your friendly BCO will merely include it in the list of things he checks for you.
The BC checking will involve establishing your foundations were good enough to support the walls, that the thermal properties are adequate, that you have made appropriate arrangements to avoid the ingress of moisture, that the roof structure is strong enough and a few more bits besides.
In the unlikley event that you haven't done this, you are likely to have a swine of a job selling the house eventually.