<< Can anyone recommend a clear finish which is especially suited for
kitchen use (hardwearing, resistant to grease and water)? >>
Polyurethanes are inherently more wear resistant than many other common
finishes. It would be logical to expect the performance you need from most any
premium floor finish. Water-based polyurethanes are said to be lighter in color
and less prone to yellowing than solvent types. Perhaps a search for bar
finishes might turn up a unique product, but IMO you won't have to look very
hard for a very good varnish. Good luck.