On Fri, 27 May 2005 05:29:38 GMT, "BigWallop"
wrote:

If the metal box is completely covered by your new boxes,

It isn't completely covered, unless it's both covered and you replace
the screws holding the cover on with insulated ones.

then why fix an earth tag to it at all?

To provide a path for a fault current, in the case of a wire coming
loose inside the box. It's not just to protect you from a live case
fault, it's to signal the occurence of this fault even before you've
touched it.