Can the group add any input or advise on the next project on my list...

Following 4 power cuts in as many weeks, and fairly frequent power failures
generally, (always at night!) I want to create a UPS protected lighting
circuit.
I already have a decent digital generator and the Briggs & Stratton
change-over switch installed, all of which works well. It's now the gap
between the power going out and me getting the generator connected & started
with no light that i'm trying to prevent.
I have an emergency light by the CU already, but SWMBO has made it clear
these are not to be fitted 'in view' around the house, which is fair enough,
therefore keeping the existing light working when the power goes out is the
way to go.

I propose to use a spare APC Smart-UPS for this that I have already, it's
one of the bigger units with sine-wave output, and in testing is fine
powering CFL's and incadecent lights etc. It's big enough for the maximum
load of every light switched on together, and has had new batteries ftted
recently.

So... I plan to use a small 2 way CU for 'UPS protected circuits' and move
the MCBs for the internal lighting circuits to there, and in turn feed this
CU via the UPS. I can mount an IEC input connector into the protected CU for
the UPS's output to connect with. In addition I plan to use a DPDT
changeover switch to allow the protected CU to be supplied by either the UPS
or the conventional CU (via a MCB), to allow normal light operation if the
UPS is not fitted etc.
The UPS's mains supply will come from a dedicated MCB in the existing CU.
I'll probably add some status neon lights to the protected CU so it's clear
which power sources are energised at a given time.
Earths will be common between all circuits. There is an earth rod in place
already.

Can anyone see any potential issues with this arrangement? Apart from being
far from conventional, is there anything wrong with it?

Once complete the lighting will remain on [or whatever it's previous state
was] when the power goes out for as long as the UPS's batteries last, which
gives time being able to see what you're doing to react to it, as required.

Thanks in advance,

Alan.