On Sun, 17 Mar 2019 02:22:09 -0700, Kevin H wrote:

New kitchen planning underway. Looks like we're going to replace a gas
hob with an induction hob requiring a 32A connection back to the CU
(photo he https://goo.gl/CGJfg3)

The CU is pretty old (1995 when the house was built). There is a spare
position but on the non-RCD protected side. I assume using this slot
would not be acceptable practice?

There are RCBOs available for that board. Probably secondhand, but they
are available.
You have one/two CB's there that arent a good fit, maybe look to get them
changed, they arent expensive.

I've noticed that the current cooker is also on the non protected side
of the CU, and given there is a combined isolation switch/13A outlet
next to the cooker I was wondering if regardless of the need to add the
induction hob this alone should be a reason to update the CU, as that
socket isn't protected by the RCD? Ignore the water heater note - the
immersion heater is no longer connected.

Like for like change, so you could use the existing arrangement. You need
to take into account the Manufacturers (of the hob) instructions, if they
call for a RCD, then it is prudent to fit one.

A final question. Any reason not to use 10mm on the 10m run to the
kitchen? Hob and oven won't be sharing a circuit.

No reason not to, but no reason to fit 10mm really, unless you are
expecting to upgrade to 50 amps or so in the future, or, it is run in
insulation.
4mm T&E may be enough, it can hold 37A clipped direct or buried in a
masonry wall.