Detached garage wiring

I have a large detached garage which is supplied from the  house via a "garage" ditribution box, underground armoured cable then into a "garage" box containing main rccd / 6a lighting breaker and 26A breaker all installed by an approved / certified electrician.

Can I, as a non professional electrician, considering the new regulations, wire the garage for 3  lighting units , and 4 x 13a doulble  power power sockets, and connect them into the supplied distrbution box without having the instalation certified?

Many  thanks for your replies and guidance on this post.