IEE regs doesn't have any height prescribed, but 110cm from floor
to bottom of socket is common and works with typical kitchen units.
Remember to allow for floor thickness if flooring isn't yet fitted.

Yes, I've used 20cm from worksurface to bottom of socket for mine (which is
the same thing given 90cm standard worksurface height). It seems to be a
reasonable compromise between having excessively trailing leads and not
having the sockets blocked by the worksurface contents.

Christian.