You don't need an earth block, they have supplied one already. (Not to mention most cus have a set of earth terminals to use)
Better to avoid extra joints.
Actually this all came about because I need to run power to an outbuilding, I have another small 2 way metal CU to be fitted (to the right of the current CU) which will supply it, I need to earth the armour of the 10mm2 2-core SWA that will be terminated in an adaptable box on the outside wall. So I need an earth block so I can run one earth to the main CU and one to the gland in the adaptable box. The DNO earth block only has capacity for one cable.