reference to first post, doesn't having an RCD fitted in the CU count as the main switch for the Installation,the CU doesn't have to have a 100Amp switch and RCD, RCD is acceptable on its own.
I agree that an Isolator of sorts should be fitted so the main DNO fuse doesn't 'fall out'.
another question leading from this, say the DNO fuse has fallen out, Can an Isolator switch be fitted and where can they be supplied from, or DO the DNO HAve to fit them.
Edit - Just reread first post and noticed 2 RCD's fitted, so unless 2nd RCD fed from 1st RCD (not good practice), then wouldn't be safe.