I would agree with the other posters, and their comments do indeed hold some weight to the argument.
This is often why electricians spend so much time at learning, before they are let loose on the open world.
However having said that if you are going to do the job then do it right, and follow any instruction very carefully, any mistake could harm or even kill someone.
Its no good thinking a cable is suitable if it can carry a certain amperage, you need to derate and allow for external influences that may effect its capacity to perform, then you have to calculate its disconnection time with the CPD you have chosen, then you have to consider diversity in calculating total demand, and if by adding this cicuit you have exceeded this demand.
So thank you for asking, and if there is any doubts then ask again, because I would rather you do it right than think its ok to do it as you feel.Or how others say it should be done.