I'm a great fan of UFH, but it must be designed, installed and controlled properly.
The bad news is .......... although solid floors give the best results (also cheaper than fitting over a suspended floor), best results are from excavating your whole ground floor to a depth of around a foot (300mm).
The reason being, insulation is essential. Heat losses under the system will be huge, and very wasteful without insulation.
Assuming a solid bed... there would be ...
100mm of concrete
50-100mm of "board" insulation (50 minimum, 100 is best)
Then plastic pipework laid over this.
Then a sand & cement screed (50mm) over this (surrounding the pipework)
Solid hardwood flooring is then glued over all.
The screed ensures an even spread of heat. Although I appreciate Jomofil's concerns over timber warping......... this should never happen with good flooring timber and a properly controlled system
Unlike rads, the floor should NOT be overly warm to the touch. The heating principle is quite different from rads. The system temperature is much lower than that used in radiators.