It's not really what you want, and I'm sure you've seen it already, but
>Screwfix sell pre-finished hardwood flooring.
Thanks for the tip. I hadn't thought of Screwfix but now you've mentioned it I've looked at their catalogue and see that they do quite a nice variety of solid hardwood flooring. I've already considered flooring for the job and may use it as one option. The downside for me is that it's on the thick side (around 19mm) and has specially formed edges for jointing purposes, which would have to go. That's why I'd prefer square edged paneling if I could find it.