Sizing cables as per BS7676.
It (tabulated cable rating)
In (protective device rating)
It > In/de-rating factors.
Therefore 70mm2 SW/PVC 4 C = 207A table 4D4A
In = 200A cg = 0.87
200A/0.87 = 229A
207>229 It is not greater than In therefore cable is not big enough for a 200A fuse, however the calculation has not flagged this as an error.
Could you please log a service ticket here and we can take your project from there?