" Thanks very much for the words of caution. If you're right that I have
to
take the doors back to bare wood, then I would hesitate at this stage to
move forwards - the original idea was that this was a relatively simple
job which could be done mostly by myself and on a budget. Adding
something like what you're suggesting causes me to wonder whether it's
worth doing at all.

The doors themselves are, from what I can see, solid wood, dark
varnished
fairly heavily and, as there are units both above and below the
worktops,
the overall effect is of a very dark kitchen. I had originally thought
that a freshly painted ceiling and units, a new light and new floor
tiles
would have the effect of a fairly significant makeover.
You can do this without too much preparation if you use a liquid, solvent
based gloss paint. Make sure the first coat is very thin and well rubbed
into the surface. It should just look slightly duller than what you
started
with when dry. From then on, you can use an oil based undercoat to get a
flat white surface, and finish off with gloss, eggshell, or whatever, but
keep it oil based throughout. Water based paints don't look good and
aren't
tough enough.
A smelly job, with 24 hours between coats, but not difficult and not
expensive.