Hi, my questions is that does a fuse box / electrical intake in a corridor in a building with two flats in it need to be covered with some fire retardant material in order to provide 30 minutes fire separation between the fuse box / electrical intake and the common corridor and the flat above?

Yes. The corridor from the front door of a flat to the final exit, is a protected route to enable people to escape safely and any fire risks have to be eliminated or protected to achieve a minimum 30 minutes fire protection. So as the electric intake cannot be eliminated it has to be protected to achieve a safe escape route.