Since having the floors replaced throughout the ground floor of our
house I have not got round to covering up the concrete under the
stairs, but now the time has come (or so I have been told).

The original plan was to put floorboards down (wickes french pine) on
battens screwed to the floor. This would bring the floor pretty level
with the indian stone flagging which it will butt up to at the cupboard
entrance.

However, on closer inspection in the corner the concrete seems to be
less thick (sounds a bit hollow) than the rest of the floor and the it
is a bit uneven and dips half an inch. I doubt the thickness will be an
issue for the traffic as we don't even walk on it, but I am a bit
reticent to drill into it to fix battens.

Ultimately we just want a half decent looking surface that is fairly
level, easy to clean and quick to fit.

In the end I took Dave's advice and used copious amounts of no more
nails to stick battens down, and plugged screwed one half where the
concrete sounded thick. The big gaps were packed and/or splinted with
18mm WPB scribed to the floor and screwed to the sides of the battens.

I finished off with Wickes french pine boards secret nailed to the
battens and trimmed with skirting.

Looks good and feels solid!

Cheers for all the suggestions,

Alex.