On Friday, 27 July 2018 15:59:39 UTC+1, Scott wrote:
On Tue, 17 Jul 2018 14:31:32 +0100, "Dave Plowman (News)"
wrote:

Just has a letter from UK Power Networks stating their records show I have
one of these which is outdated and needs to be replaced urgently.

Be interested to know why this has suddenly become urgent. ;-)

However, mine was replaced by a single line fuse with neutral link some 40
odd years ago - before I bought this house.

But the point of this post is the diagram on the letter - to allow you to
identify your unit - shows an earth terminal as being part of their
obligatory supply. Last time I checked, this wasn't the case. Have the
regs changed? Can I demand they fit one FOC?

Just to go back to basics, does anyone know why these were installed
in the first place if they were dangerous, apparently ineffective and
involved additional cost? Was it a throwback to DC supply?

In many cases yes.
Also centre tap earthing as in a tool transformer. (Both conductors were live to earth.)
I took many out as an apprentice. Or replaced the neutral fuse with a solid link