Invisible Man wrote:

I have asked my supplier whether they will convert to TNC-S and am
awaiting a reply. Can anyone comment on my chances of getting the supply
changed over? EDF Energy area but my supplier is Atlantic Electricity
and Gas.

Fairly likely, unless you're in the back of beyond. It might help to
ask for 'PME conversion' rather than TNC-S, although it's exactly the
same thing of course. You may have to pay. With an older TT
installation you'll probably need to add or upgrade the main bonding,
otherwise connection of your earthing conductor to the PME terminal will
be refused.

DIY bit if I have to stick with TT.
The solid porch floor needs re-tiling with another layer of ceramic
tiles on top of existing. To get an earth to an earth rod in a suitable
area it would need to cross the porch.
Can I cut a channel for the earth wire in the floor and lay conduit for
an electrician to use when the rod is moved? If so how deep does it need
to be and does it need to be covered by anything special?

Sounds OK. The earthing conductor to the rod will need to be 16 mm^2 if
it will be buried in the ground once outside. This will easily go
through 20 mm PVC conduit for a a straight run, but you'll need a larger
duct if there are many bends. There's no specific rule for depth in a
solid floor, other than "sufficient to avoid damage due to any
foreseeable disturbance".

--
Andy